#12586: add provisional email policy with new header parsing and folding.

When the new policies are used (and only when the new policies are explicitly
used) headers turn into objects that have attributes based on their parsed
values, and can be set using objects that encapsulate the values, as well as
set directly from unicode strings.  The folding algorithm then takes care of
encoding unicode where needed, and folding according to the highest level
syntactic objects.

With this patch only date and time headers are parsed as anything other than
unstructured, but that is all the helper methods in the existing API handle.
I do plan to add more parsers, and complete the set specified in the RFC
before the package becomes stable.

16 files changed, 6994 insertions, 116 deletions

diff --git a/Doc/library/email.policy.rst b/Doc/library/email.policy.rst
index 73cfba1..c65130b 100644
--- a/Doc/library/email.policy.rst
+++ b/Doc/library/email.policy.rst
@@ -306,3 +306,326 @@ added matters.  To illustrate::
       ``7bit``, non-ascii binary data is CTE encoded using the ``unknown-8bit``
       charset.  Otherwise the original source header is used, with its existing
       line breaks and and any (RFC invalid) binary data it may contain.
+
+
+.. note::
+
+   The remainder of the classes documented below are included in the standard
+   library on a :term:`provisional basis <provisional package>`.  Backwards
+   incompatible changes (up to and including removal of the feature) may occur
+   if deemed necessary by the core developers.
+
+
+.. class:: EmailPolicy(**kw)
+
+   This concrete :class:`Policy` provides behavior that is intended to be fully
+   compliant with the current email RFCs.  These include (but are not limited
+   to) :rfc:`5322`, :rfc:`2047`, and the current MIME RFCs.
+
+   This policy adds new header parsing and folding algorithms.  Instead of
+   simple strings, headers are custom objects with custom attributes depending
+   on the type of the field.  The parsing and folding algorithm fully implement
+   :rfc:`2047` and :rfc:`5322`.
+
+   In addition to the settable attributes listed above that apply to all
+   policies, this policy adds the following additional attributes:
+
+   .. attribute:: refold_source
+
+      If the value for a header in the ``Message`` object originated from a
+      :mod:`~email.parser` (as opposed to being set by a program), this
+      attribute indicates whether or not a generator should refold that value
+      when transforming the message back into stream form.  The possible values
+      are:
+
+      ========  ===============================================================
+      ``none``  all source values use original folding
+
+      ``long``  source values that have any line that is longer than
+                ``max_line_length`` will be refolded
+
+      ``all``   all values are refolded.
+      ========  ===============================================================
+
+      The default is ``long``.
+
+   .. attribute:: header_factory
+
+      A callable that takes two arguments, ``name`` and ``value``, where
+      ``name`` is a header field name and ``value`` is an unfolded header field
+      value, and returns a string-like object that represents that header.  A
+      default ``header_factory`` is provided that understands some of the
+      :RFC:`5322` header field types.  (Currently address fields and date
+      fields have special treatment, while all other fields are treated as
+      unstructured.  This list will be completed before the extension is marked
+      stable.)
+
+   The class provides the following concrete implementations of the abstract
+   methods of :class:`Policy`:
+
+   .. method:: header_source_parse(sourcelines)
+
+      The implementation of this method is the same as that for the
+      :class:`Compat32` policy.
+
+   .. method:: header_store_parse(name, value)
+
+      The name is returned unchanged.  If the input value has a ``name``
+      attribute and it matches *name* ignoring case, the value is returned
+      unchanged.  Otherwise the *name* and *value* are passed to
+      ``header_factory``, and the resulting custom header object is returned as
+      the value.  In this case a ``ValueError`` is raised if the input value
+      contains CR or LF characters.
+
+   .. method:: header_fetch_parse(name, value)
+
+      If the value has a ``name`` attribute, it is returned to unmodified.
+      Otherwise the *name*, and the *value* with any CR or LF characters
+      removed, are passed to the ``header_factory``, and the resulting custom
+      header object is returned.  Any surrogateescaped bytes get turned into
+      the unicode unknown-character glyph.
+
+   .. method:: fold(name, value)
+
+      Header folding is controlled by the :attr:`refold_source` policy setting.
+      A value is considered to be a 'source value' if and only if it does not
+      have a ``name`` attribute (having a ``name`` attribute means it is a
+      header object of some sort).  If a source value needs to be refolded
+      according to the policy, it is converted into a custom header object by
+      passing the *name* and the *value* with any CR and LF characters removed
+      to the ``header_factory``.  Folding of a custom header object is done by
+      calling its ``fold`` method with the current policy.
+
+      Source values are split into lines using :meth:`~str.splitlines`.  If
+      the value is not to be refolded, the lines are rejoined using the
+      ``linesep`` from the policy and returned.  The exception is lines
+      containing non-ascii binary data.  In that case the value is refolded
+      regardless of the ``refold_source`` setting, which causes the binary data
+      to be CTE encoded using the ``unknown-8bit`` charset.
+
+   .. method:: fold_binary(name, value)
+
+      The same as :meth:`fold` if :attr:`cte_type` is ``7bit``, except that
+      the returned value is bytes.
+
+      If :attr:`cte_type` is ``8bit``, non-ASCII binary data is converted back
+      into bytes.  Headers with binary data are not refolded, regardless of the
+      ``refold_header`` setting, since there is no way to know whether the
+      binary data consists of single byte characters or multibyte characters.
+
+The following instances of :class:`EmailPolicy` provide defaults suitable for
+specific application domains.  Note that in the future the behavior of these
+instances (in particular the ``HTTP` instance) may be adjusted to conform even
+more closely to the RFCs relevant to their domains.
+
+.. data:: default
+
+   An instance of ``EmailPolicy`` with all defaults unchanged.  This policy
+   uses the standard Python ``\n`` line endings rather than the RFC-correct
+   ``\r\n``.
+
+.. data:: SMTP
+
+   Suitable for serializing messages in conformance with the email RFCs.
+   Like ``default``, but with ``linesep`` set to ``\r\n``, which is RFC
+   compliant.
+
+.. data:: HTTP
+
+   Suitable for serializing headers with for use in HTTP traffic.  Like
+   ``SMTP`` except that ``max_line_length`` is set to ``None`` (unlimited).
+
+.. data:: strict
+
+   Convenience instance.  The same as ``default`` except that
+   ``raise_on_defect`` is set to ``True``.  This allows any policy to be made
+   strict by writing::
+
+        somepolicy + policy.strict
+
+With all of these :class:`EmailPolicies <.EmailPolicy>`, the effective API of
+the email package is changed from the Python 3.2 API in the following ways:
+
+   * Setting a header on a :class:`~email.message.Message` results in that
+     header being parsed and a custom header object created.
+
+   * Fetching a header value from a :class:`~email.message.Message` results
+     in that header being parsed and a custom header object created and
+     returned.
+
+   * Any custom header object, or any header that is refolded due to the
+     policy settings, is folded using an algorithm that fully implements the
+     RFC folding algorithms, including knowing where encoded words are required
+     and allowed.
+
+From the application view, this means that any header obtained through the
+:class:`~email.message.Message` is a custom header object with custom
+attributes, whose string value is the fully decoded unicode value of the
+header.  Likewise, a header may be assigned a new value, or a new header
+created, using a unicode string, and the policy will take care of converting
+the unicode string into the correct RFC encoded form.
+
+The custom header objects and their attributes are described below.  All custom
+header objects are string subclasses, and their string value is the fully
+decoded value of the header field (the part of the field after the ``:``)
+
+
+.. class:: BaseHeader
+
+   This is the base class for all custom header objects.  It provides the
+   following attributes:
+
+   .. attribute:: name
+
+      The header field name (the portion of the field before the ':').
+
+   .. attribute:: defects
+
+      A possibly empty list of :class:`~email.errors.MessageDefect` objects
+      that record any RFC violations found while parsing the header field.
+
+   .. method:: fold(*, policy)
+
+      Return a string containing :attr:`~email.policy.Policy.linesep`
+      characters as required to correctly fold the header according
+      to *policy*.  A :attr:`~email.policy.Policy.cte_type` of
+      ``8bit`` will be treated as if it were ``7bit``, since strings
+      may not contain binary data.
+
+
+.. class:: UnstructuredHeader
+
+   The class used for any header that does not have a more specific
+   type.  (The :mailheader:`Subject` header is an example of an
+   unstructured header.)  It does not have any additional attributes.
+
+
+.. class:: DateHeader
+
+   The value of this type of header is a single date and time value.  The
+   primary example of this type of header is the :mailheader:`Date` header.
+
+   .. attribute:: datetime
+
+      A :class:`~datetime.datetime` encoding the date and time from the
+      header value.
+
+      The ``datetime`` will be a naive ``datetime`` if the value either does
+      not have a specified timezone (which would be a violation of the RFC) or
+      if the timezone is specified as ``-0000``.  This timezone value indicates
+      that the date and time is to be considered to be in UTC, but with no
+      indication of the local timezone in which it was generated.  (This
+      contrasts to ``+0000``, which indicates a date and time that really is in
+      the UTC ``0000`` timezone.)
+
+      If the header value contains a valid timezone that is not ``-0000``, the
+      ``datetime`` will be an aware ``datetime`` having a
+      :class:`~datetime.tzinfo` set to the :class:`~datetime.timezone`
+      indicated by the header value.
+
+   A ``datetime`` may also be assigned to a :mailheader:`Date` type header.
+   The resulting string value will use a timezone of ``-0000`` if the
+   ``datetime`` is naive, and the appropriate UTC offset if the ``datetime`` is
+   aware.
+
+
+.. class:: AddressHeader
+
+   This class is used for all headers that can contain addresses, whether they
+   are supposed to be singleton addresses or a list.
+
+   .. attribute:: addresses
+
+      A list of :class:`.Address` objects listing all of the addresses that
+      could be parsed out of the field value.
+
+   .. attribute:: groups
+
+      A list of :class:`.Group` objects.  Every address in :attr:`.addresses`
+      appears in one of the group objects in the tuple.  Addresses that are not
+      syntactically part of a group are represented by ``Group`` objects whose
+      ``name`` is ``None``.
+
+   In addition to addresses in string form, any combination of
+   :class:`.Address` and :class:`.Group` objects, singly or in a list, may be
+   assigned to an address header.
+
+
+.. class:: Address(display_name='', username='', domain='', addr_spec=None):
+
+   The class used to represent an email address.  The general form of an
+   address is::
+
+      [display_name] <username@domain>
+
+   or::
+
+      username@domain
+
+   where each part must conform to specific syntax rules spelled out in
+   :rfc:`5322`.
+
+   As a convenience *addr_spec* can be specified instead of *username* and
+   *domain*, in which case *username* and *domain* will be parsed from the
+   *addr_spec*.  An *addr_spec* must be a properly RFC quoted string; if it is
+   not ``Address`` will raise an error.  Unicode characters are allowed and
+   will be property encoded when serialized.  However, per the RFCs, unicode is
+   *not* allowed in the username portion of the address.
+
+   .. attribute:: display_name
+
+      The display name portion of the address, if any, with all quoting
+      removed.  If the address does not have a display name, this attribute
+      will be an empty string.
+
+   .. attribute:: username
+
+      The ``username`` portion of the address, with all quoting removed.
+
+   .. attribute:: domain
+
+      The ``domain`` portion of the address.
+
+   .. attribute:: addr_spec
+
+      The ``username@domain`` portion of the address, correctly quoted
+      for use as a bare address (the second form shown above).  This
+      attribute is not mutable.
+
+   .. method:: __str__()
+
+      The ``str`` value of the object is the address quoted according to
+      :rfc:`5322` rules, but with no Content Transfer Encoding of any non-ASCII
+      characters.
+
+
+.. class:: Group(display_name=None, addresses=None)
+
+   The class used to represent an address group.  The general form of an
+   address group is::
+
+     display_name: [address-list];
+
+   As a convenience for processing lists of addresses that consist of a mixture
+   of groups and single addresses, a ``Group`` may also be used to represent
+   single addresses that are not part of a group by setting *display_name* to
+   ``None`` and providing a list of the single address as *addresses*.
+
+   .. attribute:: display_name
+
+      The ``display_name`` of the group.  If it is ``None`` and there is
+      exactly one ``Address`` in ``addresses``, then the ``Group`` represents a
+      single address that is not in a group.
+
+   .. attribute:: addresses
+
+      A possibly empty tuple of :class:`.Address` objects representing the
+      addresses in the group.
+
+   .. method:: __str__()
+
+      The ``str`` value of a ``Group`` is formatted according to :rfc:`5322`,
+      but with no Content Transfer Encoding of any non-ASCII characters.  If
+      ``display_name`` is none and there is a single ``Address`` in the
+      ``addresses` list, the ``str`` value will be the same as the ``str`` of
+      that single ``Address``.
diff --git a/Lib/email/_encoded_words.py b/Lib/email/_encoded_words.py
new file mode 100644
index 0000000..01fe42f
--- /dev/null
+++ b/Lib/email/_encoded_words.py
@@ -0,0 +1,211 @@
+""" Routines for manipulating RFC2047 encoded words.
+
+This is currently a package-private API, but will be considered for promotion
+to a public API if there is demand.
+
+"""
+
+# An ecoded word looks like this:
+#
+#        =?charset[*lang]?cte?encoded_string?=
+#
+# for more information about charset see the charset module.  Here it is one
+# of the preferred MIME charset names (hopefully; you never know when parsing).
+# cte (Content Transfer Encoding) is either 'q' or 'b' (ignoring case).  In
+# theory other letters could be used for other encodings, but in practice this
+# (almost?) never happens.  There could be a public API for adding entries
+# to to the CTE tables, but YAGNI for now.  'q' is Quoted Printable, 'b' is
+# Base64.  The meaning of encoded_string should be obvious.  'lang' is optional
+# as indicated by the brackets (they are not part of the syntax) but is almost
+# never encountered in practice.
+#
+# The general interface for a CTE decoder is that it takes the encoded_string
+# as its argument, and returns a tuple (cte_decoded_string, defects).  The
+# cte_decoded_string is the original binary that was encoded using the
+# specified cte.  'defects' is a list of MessageDefect instances indicating any
+# problems encountered during conversion.  'charset' and 'lang' are the
+# corresponding strings extracted from the EW, case preserved.
+#
+# The general interface for a CTE encoder is that it takes a binary sequence
+# as input and returns the cte_encoded_string, which is an ascii-only string.
+#
+# Each decoder must also supply a length function that takes the binary
+# sequence as its argument and returns the length of the resulting encoded
+# string.
+#
+# The main API functions for the module are decode, which calls the decoder
+# referenced by the cte specifier, and encode, which adds the appropriate
+# RFC 2047 "chrome" to the encoded string, and can optionally automatically
+# select the shortest possible encoding.  See their docstrings below for
+# details.
+
+import re
+import base64
+import binascii
+import functools
+from string import ascii_letters, digits
+from email import errors
+
+#
+# Quoted Printable
+#
+
+# regex based decoder.
+_q_byte_subber = functools.partial(re.compile(br'=([a-fA-F0-9]{2})').sub,
+        lambda m: bytes([int(m.group(1), 16)]))
+
+def decode_q(encoded):
+    encoded = encoded.replace(b'_', b' ')
+    return _q_byte_subber(encoded), []
+
+
+# dict mapping bytes to their encoded form
+class QByteMap(dict):
+
+    safe = b'-!*+/' + ascii_letters.encode('ascii') + digits.encode('ascii')
+
+    def __missing__(self, key):
+        if key in self.safe:
+            self[key] = chr(key)
+        else:
+            self[key] = "={:02X}".format(key)
+        return self[key]
+
+_q_byte_map = QByteMap()
+
+# In headers spaces are mapped to '_'.
+_q_byte_map[ord(' ')] = '_'
+
+def encode_q(bstring):
+    return ''.join(_q_byte_map[x] for x in bstring)
+
+def len_q(bstring):
+    return sum(len(_q_byte_map[x]) for x in bstring)
+
+
+#
+# Base64
+#
+
+def decode_b(encoded):
+    defects = []
+    pad_err = len(encoded) % 4
+    if pad_err:
+        defects.append(errors.InvalidBase64PaddingDefect())
+        padded_encoded = encoded + b'==='[:4-pad_err]
+    else:
+        padded_encoded = encoded
+    try:
+        return base64.b64decode(padded_encoded, validate=True), defects
+    except binascii.Error:
+        # Since we had correct padding, this must an invalid char error.
+        defects = [errors.InvalidBase64CharactersDefect()]
+        # The non-alphabet characters are ignored as far as padding
+        # goes, but we don't know how many there are.  So we'll just
+        # try various padding lengths until something works.
+        for i in 0, 1, 2, 3:
+            try:
+                return base64.b64decode(encoded+b'='*i, validate=False), defects
+            except binascii.Error:
+                if i==0:
+                    defects.append(errors.InvalidBase64PaddingDefect())
+        else:
+            # This should never happen.
+            raise AssertionError("unexpected binascii.Error")
+
+def encode_b(bstring):
+    return base64.b64encode(bstring).decode('ascii')
+
+def len_b(bstring):
+    groups_of_3, leftover = divmod(len(bstring), 3)
+    # 4 bytes out for each 3 bytes (or nonzero fraction thereof) in.
+    return groups_of_3 * 4 + (4 if leftover else 0)
+
+
+_cte_decoders = {
+    'q': decode_q,
+    'b': decode_b,
+    }
+
+def decode(ew):
+    """Decode encoded word and return (string, charset, lang, defects) tuple.
+
+    An RFC 2047/2243 encoded word has the form:
+
+        =?charset*lang?cte?encoded_string?=
+
+    where '*lang' may be omitted but the other parts may not be.
+
+    This function expects exactly such a string (that is, it does not check the
+    syntax and may raise errors if the string is not well formed), and returns
+    the encoded_string decoded first from its Content Transfer Encoding and
+    then from the resulting bytes into unicode using the specified charset.  If
+    the cte-decoded string does not successfully decode using the specified
+    character set, a defect is added to the defects list and the unknown octets
+    are replaced by the unicode 'unknown' character \uFDFF.
+
+    The specified charset and language are returned.  The default for language,
+    which is rarely if ever encountered, is the empty string.
+
+    """
+    _, charset, cte, cte_string, _ = ew.split('?')
+    charset, _, lang = charset.partition('*')
+    cte = cte.lower()
+    # Recover the original bytes and do CTE decoding.
+    bstring = cte_string.encode('ascii', 'surrogateescape')
+    bstring, defects = _cte_decoders[cte](bstring)
+    # Turn the CTE decoded bytes into unicode.
+    try:
+        string = bstring.decode(charset)
+    except UnicodeError:
+        defects.append(errors.UndecodableBytesDefect("Encoded word "
+            "contains bytes not decodable using {} charset".format(charset)))
+        string = bstring.decode(charset, 'surrogateescape')
+    except LookupError:
+        string = bstring.decode('ascii', 'surrogateescape')
+        if charset.lower() != 'unknown-8bit':
+            defects.append(errors.CharsetError("Unknown charset {} "
+                "in encoded word; decoded as unknown bytes".format(charset)))
+    return string, charset, lang, defects
+
+
+_cte_encoders = {
+    'q': encode_q,
+    'b': encode_b,
+    }
+
+_cte_encode_length = {
+    'q': len_q,
+    'b': len_b,
+    }
+
+def encode(string, charset='utf-8', encoding=None, lang=''):
+    """Encode string using the CTE encoding that produces the shorter result.
+
+    Produces an RFC 2047/2243 encoded word of the form:
+
+        =?charset*lang?cte?encoded_string?=
+
+    where '*lang' is omitted unless the 'lang' parameter is given a value.
+    Optional argument charset (defaults to utf-8) specifies the charset to use
+    to encode the string to binary before CTE encoding it.  Optional argument
+    'encoding' is the cte specifier for the encoding that should be used ('q'
+    or 'b'); if it is None (the default) the encoding which produces the
+    shortest encoded sequence is used, except that 'q' is preferred if it is up
+    to five characters longer.  Optional argument 'lang' (default '') gives the
+    RFC 2243 language string to specify in the encoded word.
+
+    """
+    if charset == 'unknown-8bit':
+        bstring = string.encode('ascii', 'surrogateescape')
+    else:
+        bstring = string.encode(charset)
+    if encoding is None:
+        qlen = _cte_encode_length['q'](bstring)
+        blen = _cte_encode_length['b'](bstring)
+        # Bias toward q.  5 is arbitrary.
+        encoding = 'q' if qlen - blen < 5 else 'b'
+    encoded = _cte_encoders[encoding](bstring)
+    if lang:
+        lang = '*' + lang
+    return "=?{}{}?{}?{}?=".format(charset, lang, encoding, encoded)
diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
new file mode 100644
index 0000000..87d8f68
--- /dev/null
+++ b/Lib/email/_header_value_parser.py
@@ -0,0 +1,2145 @@
+"""Header value parser implementing various email-related RFC parsing rules.
+
+The parsing methods defined in this module implement various email related
+parsing rules.  Principal among them is RFC 5322, which is the followon
+to RFC 2822 and primarily a clarification of the former.  It also implements
+RFC 2047 encoded word decoding.
+
+RFC 5322 goes to considerable trouble to maintain backward compatibility with
+RFC 822 in the parse phase, while cleaning up the structure on the generation
+phase.  This parser supports correct RFC 5322 generation by tagging white space
+as folding white space only when folding is allowed in the non-obsolete rule
+sets.  Actually, the parser is even more generous when accepting input than RFC
+5322 mandates, following the spirit of Postel's Law, which RFC 5322 encourages.
+Where possible deviations from the standard are annotated on the 'defects'
+attribute of tokens that deviate.
+
+The general structure of the parser follows RFC 5322, and uses its terminology
+where there is a direct correspondence.  Where the implementation requires a
+somewhat different structure than that used by the formal grammar, new terms
+that mimic the closest existing terms are used.  Thus, it really helps to have
+a copy of RFC 5322 handy when studying this code.
+
+Input to the parser is a string that has already been unfolded according to
+RFC 5322 rules.  According to the RFC this unfolding is the very first step, and
+this parser leaves the unfolding step to a higher level message parser, which
+will have already detected the line breaks that need unfolding while
+determining the beginning and end of each header.
+
+The output of the parser is a TokenList object, which is a list subclass.  A
+TokenList is a recursive data structure.  The terminal nodes of the structure
+are Terminal objects, which are subclasses of str.  These do not correspond
+directly to terminal objects in the formal grammar, but are instead more
+practical higher level combinations of true terminals.
+
+All TokenList and Terminal objects have a 'value' attribute, which produces the
+semantically meaningful value of that part of the parse subtree.  The value of
+all whitespace tokens (no matter how many sub-tokens they may contain) is a
+single space, as per the RFC rules.  This includes 'CFWS', which is herein
+included in the general class of whitespace tokens.  There is one exception to
+the rule that whitespace tokens are collapsed into single spaces in values: in
+the value of a 'bare-quoted-string' (a quoted-string with no leading or
+trailing whitespace), any whitespace that appeared between the quotation marks
+is preserved in the returned value.  Note that in all Terminal strings quoted
+pairs are turned into their unquoted values.
+
+All TokenList and Terminal objects also have a string value, which attempts to
+be a "canonical" representation of the RFC-compliant form of the substring that
+produced the parsed subtree, including minimal use of quoted pair quoting.
+Whitespace runs are not collapsed.
+
+Comment tokens also have a 'content' attribute providing the string found
+between the parens (including any nested comments) with whitespace preserved.
+
+All TokenList and Terminal objects have a 'defects' attribute which is a
+possibly empty list all of the defects found while creating the token.  Defects
+may appear on any token in the tree, and a composite list of all defects in the
+subtree is available through the 'all_defects' attribute of any node.  (For
+Terminal notes x.defects == x.all_defects.)
+
+Each object in a parse tree is called a 'token', and each has a 'token_type'
+attribute that gives the name from the RFC 5322 grammar that it represents.
+Not all RFC 5322 nodes are produced, and there is one non-RFC 5322 node that
+may be produced: 'ptext'.  A 'ptext' is a string of printable ascii characters.
+It is returned in place of lists of (ctext/quoted-pair) and
+(qtext/quoted-pair).
+
+XXX: provide complete list of token types.
+"""
+
+import re
+from email import _encoded_words as _ew
+from email import errors
+from email import utils
+
+#
+# Useful constants and functions
+#
+
+WSP = set(' \t')
+CFWS_LEADER = WSP | set('(')
+SPECIALS = set(r'()<>@,:;.\"[]')
+ATOM_ENDS = SPECIALS | WSP
+DOT_ATOM_ENDS = ATOM_ENDS - set('.')
+# '.', '"', and '(' do not end phrases in order to support obs-phrase
+PHRASE_ENDS = SPECIALS - set('."(')
+
+def quote_string(value):
+    return '"'+str(value).replace('\\', '\\\\').replace('"', r'\"')+'"'
+
+#
+# Accumulator for header folding
+#
+
+class _Folded:
+
+    def __init__(self, maxlen, policy):
+        self.maxlen = maxlen
+        self.policy = policy
+        self.lastlen = 0
+        self.stickyspace = None
+        self.firstline = True
+        self.done = []
+        self.current = []
+
+    def newline(self):
+        self.done.extend(self.current)
+        self.done.append(self.policy.linesep)
+        self.current.clear()
+        self.lastlen = 0
+
+    def finalize(self):
+        if self.current:
+            self.newline()
+
+    def __str__(self):
+        return ''.join(self.done)
+
+    def append(self, stoken):
+        self.current.append(stoken)
+
+    def append_if_fits(self, token, stoken=None):
+        if stoken is None:
+            stoken = str(token)
+        l = len(stoken)
+        if self.stickyspace is not None:
+            stickyspace_len = len(self.stickyspace)
+            if self.lastlen + stickyspace_len + l <= self.maxlen:
+                self.current.append(self.stickyspace)
+                self.lastlen += stickyspace_len
+                self.current.append(stoken)
+                self.lastlen += l
+                self.stickyspace = None
+                self.firstline = False
+                return True
+            if token.has_fws:
+                ws = token.pop_leading_fws()
+                if ws is not None:
+                    self.stickyspace += str(ws)
+                    stickyspace_len += len(ws)
+                token._fold(self)
+                return True
+            if stickyspace_len and l + 1 <= self.maxlen:
+                margin = self.maxlen - l
+                if 0 < margin < stickyspace_len:
+                    trim = stickyspace_len - margin
+                    self.current.append(self.stickyspace[:trim])
+                    self.stickyspace = self.stickyspace[trim:]
+                    stickyspace_len = trim
+                self.newline()
+                self.current.append(self.stickyspace)
+                self.current.append(stoken)
+                self.lastlen = l + stickyspace_len
+                self.stickyspace = None
+                self.firstline = False
+                return True
+            if not self.firstline:
+                self.newline()
+            self.current.append(self.stickyspace)
+            self.current.append(stoken)
+            self.stickyspace = None
+            self.firstline = False
+            return True
+        if self.lastlen + l <= self.maxlen:
+            self.current.append(stoken)
+            self.lastlen += l
+            return True
+        if l < self.maxlen:
+            self.newline()
+            self.current.append(stoken)
+            self.lastlen = l
+            return True
+        return False
+
+#
+# TokenList and its subclasses
+#
+
+class TokenList(list):
+
+    token_type = None
+
+    def __init__(self, *args, **kw):
+        super().__init__(*args, **kw)
+        self.defects = []
+
+    def __str__(self):
+        return ''.join(str(x) for x in self)
+
+    def __repr__(self):
+        return '{}({})'.format(self.__class__.__name__,
+                             super().__repr__())
+
+    @property
+    def value(self):
+        return ''.join(x.value for x in self if x.value)
+
+    @property
+    def all_defects(self):
+        return sum((x.all_defects for x in self), self.defects)
+
+    #
+    # Folding API
+    #
+    # parts():
+    #
+    # return a list of objects that constitute the "higher level syntactic
+    # objects" specified by the RFC as the best places to fold a header line.
+    # The returned objects must include leading folding white space, even if
+    # this means mutating the underlying parse tree of the object.  Each object
+    # is only responsible for returning *its* parts, and should not drill down
+    # to any lower level except as required to meet the leading folding white
+    # space constraint.
+    #
+    # _fold(folded):
+    #
+    #   folded: the result accumulator.  This is an instance of _Folded.
+    #       (XXX: I haven't finished factoring this out yet, the folding code
+    #       pretty much uses this as a state object.) When the folded.current
+    #       contains as much text as will fit, the _fold method should call
+    #       folded.newline.
+    #  folded.lastlen: the current length of the test stored in folded.current.
+    #  folded.maxlen: The maximum number of characters that may appear on a
+    #       folded line.  Differs from the policy setting in that "no limit" is
+    #       represented by +inf, which means it can be used in the trivially
+    #       logical fashion in comparisons.
+    #
+    # Currently no subclasses implement parts, and I think this will remain
+    # true.  A subclass only needs to implement _fold when the generic version
+    # isn't sufficient.  _fold will need to be implemented primarily when it is
+    # possible for encoded words to appear in the specialized token-list, since
+    # there is no generic algorithm that can know where exactly the encoded
+    # words are allowed.  A _fold implementation is responsible for filling
+    # lines in the same general way that the top level _fold does. It may, and
+    # should, call the _fold method of sub-objects in a similar fashion to that
+    # of the top level _fold.
+    #
+    # XXX: I'm hoping it will be possible to factor the existing code further
+    # to reduce redundancy and make the logic clearer.
+
+    @property
+    def parts(self):
+        klass = self.__class__
+        this = []
+        for token in self:
+            if token.startswith_fws():
+                if this:
+                    yield this[0] if len(this)==1 else klass(this)
+                    this.clear()
+            end_ws = token.pop_trailing_ws()
+            this.append(token)
+            if end_ws:
+                yield klass(this)
+                this = [end_ws]
+        if this:
+            yield this[0] if len(this)==1 else klass(this)
+
+    def startswith_fws(self):
+        return self[0].startswith_fws()
+
+    def pop_leading_fws(self):
+        if self[0].token_type == 'fws':
+            return self.pop(0)
+        return self[0].pop_leading_fws()
+
+    def pop_trailing_ws(self):
+        if self[-1].token_type == 'cfws':
+            return self.pop(-1)
+        return self[-1].pop_trailing_ws()
+
+    @property
+    def has_fws(self):
+        for part in self:
+            if part.has_fws:
+                return True
+        return False
+
+    def has_leading_comment(self):
+        return self[0].has_leading_comment()
+
+    @property
+    def comments(self):
+        comments = []
+        for token in self:
+            comments.extend(token.comments)
+        return comments
+
+    def fold(self, *, policy):
+        # max_line_length 0/None means no limit, ie: infinitely long.
+        maxlen = policy.max_line_length or float("+inf")
+        folded = _Folded(maxlen, policy)
+        self._fold(folded)
+        folded.finalize()
+        return str(folded)
+
+    def as_encoded_word(self, charset):
+        # This works only for things returned by 'parts', which include
+        # the leading fws, if any, that should be used.
+        res = []
+        ws = self.pop_leading_fws()
+        if ws:
+            res.append(ws)
+        trailer = self.pop(-1) if self[-1].token_type=='fws' else ''
+        res.append(_ew.encode(str(self), charset))
+        res.append(trailer)
+        return ''.join(res)
+
+    def cte_encode(self, charset, policy):
+        res = []
+        for part in self:
+            res.append(part.cte_encode(charset, policy))
+        return ''.join(res)
+
+    def _fold(self, folded):
+        for part in self.parts:
+            tstr = str(part)
+            tlen = len(tstr)
+            try:
+                str(part).encode('us-ascii')
+            except UnicodeEncodeError:
+                if any(isinstance(x, errors.UndecodableBytesDefect)
+                        for x in part.all_defects):
+                    charset = 'unknown-8bit'
+                else:
+                    # XXX: this should be a policy setting
+                    charset = 'utf-8'
+                tstr = part.cte_encode(charset, folded.policy)
+                tlen = len(tstr)
+            if folded.append_if_fits(part, tstr):
+                continue
+            # Peel off the leading whitespace if any and make it sticky, to
+            # avoid infinite recursion.
+            ws = part.pop_leading_fws()
+            if ws is not None:
+                # Peel off the leading whitespace and make it sticky, to
+                # avoid infinite recursion.
+                folded.stickyspace = str(part.pop(0))
+                if folded.append_if_fits(part):
+                    continue
+            if part.has_fws:
+                part._fold(folded)
+                continue
+            # There are no fold points in this one; it is too long for a single
+            # line and can't be split...we just have to put it on its own line.
+            folded.append(tstr)
+            folded.newline()
+
+    def pprint(self, indent=''):
+        print('\n'.join(self._pp(indent='')))
+
+    def ppstr(self, indent=''):
+        return '\n'.join(self._pp(indent=''))
+
+    def _pp(self, indent=''):
+        yield '{}{}/{}('.format(
+            indent,
+            self.__class__.__name__,
+            self.token_type)
+        for token in self:
+            for line in token._pp(indent+'    '):
+                yield line
+        if self.defects:
+            extra = ' Defects: {}'.format(self.defects)
+        else:
+            extra = ''
+        yield '{}){}'.format(indent, extra)
+
+
+class WhiteSpaceTokenList(TokenList):
+
+    @property
+    def value(self):
+        return ' '
+
+    @property
+    def comments(self):
+        return [x.content for x in self if x.token_type=='comment']
+
+
+class UnstructuredTokenList(TokenList):
+
+    token_type = 'unstructured'
+
+    def _fold(self, folded):
+        if any(x.token_type=='encoded-word' for x in self):
+            return self._fold_encoded(folded)
+        # Here we can have either a pure ASCII string that may or may not
+        # have surrogateescape encoded bytes, or a unicode string.
+        last_ew = None
+        for part in self.parts:
+            tstr = str(part)
+            is_ew = False
+            try:
+                str(part).encode('us-ascii')
+            except UnicodeEncodeError:
+                if any(isinstance(x, errors.UndecodableBytesDefect)
+                       for x in part.all_defects):
+                    charset = 'unknown-8bit'
+                else:
+                    charset = 'utf-8'
+                if last_ew is not None:
+                    # We've already done an EW, combine this one with it
+                    # if there's room.
+                    chunk = get_unstructured(
+                        ''.join(folded.current[last_ew:]+[tstr])).as_encoded_word(charset)
+                    oldlastlen = sum(len(x) for x in folded.current[:last_ew])
+                    schunk = str(chunk)
+                    lchunk = len(schunk)
+                    if oldlastlen + lchunk <= folded.maxlen:
+                        del folded.current[last_ew:]
+                        folded.append(schunk)
+                        folded.lastlen = oldlastlen + lchunk
+                        continue
+                tstr = part.as_encoded_word(charset)
+                is_ew = True
+            if folded.append_if_fits(part, tstr):
+                if is_ew:
+                    last_ew = len(folded.current) - 1
+                continue
+            if is_ew or last_ew:
+                # It's too big to fit on the line, but since we've
+                # got encoded words we can use encoded word folding.
+                part._fold_as_ew(folded)
+                continue
+            # Peel off the leading whitespace if any and make it sticky, to
+            # avoid infinite recursion.
+            ws = part.pop_leading_fws()
+            if ws is not None:
+                folded.stickyspace = str(ws)
+                if folded.append_if_fits(part):
+                    continue
+            if part.has_fws:
+                part.fold(folded)
+                continue
+            # It can't be split...we just have to put it on its own line.
+            folded.append(tstr)
+            folded.newline()
+            last_ew = None
+
+    def cte_encode(self, charset, policy):
+        res = []
+        last_ew = None
+        for part in self:
+            spart = str(part)
+            try:
+                spart.encode('us-ascii')
+                res.append(spart)
+            except UnicodeEncodeError:
+                if last_ew is None:
+                    res.append(part.cte_encode(charset, policy))
+                    last_ew = len(res)
+                else:
+                    tl = get_unstructured(''.join(res[last_ew:] + [spart]))
+                    res.append(tl.as_encoded_word())
+        return ''.join(res)
+
+
+class Phrase(TokenList):
+
+    token_type = 'phrase'
+
+    def _fold(self, folded):
+        # As with Unstructured, we can have pure ASCII with or without
+        # surrogateescape encoded bytes, or we could have unicode.  But this
+        # case is more complicated, since we have to deal with the various
+        # sub-token types and how they can be composed in the face of
+        # unicode-that-needs-CTE-encoding, and the fact that if a token a
+        # comment that becomes a barrier across which we can't compose encoded
+        # words.
+        last_ew = None
+        for part in self.parts:
+            tstr = str(part)
+            tlen = len(tstr)
+            has_ew = False
+            try:
+                str(part).encode('us-ascii')
+            except UnicodeEncodeError:
+                if any(isinstance(x, errors.UndecodableBytesDefect)
+                        for x in part.all_defects):
+                    charset = 'unknown-8bit'
+                else:
+                    charset = 'utf-8'
+                if last_ew is not None and not part.has_leading_comment():
+                    # We've already done an EW, let's see if we can combine
+                    # this one with it.  The last_ew logic ensures that all we
+                    # have at this point is atoms, no comments or quoted
+                    # strings.  So we can treat the text between the last
+                    # encoded word and the content of this token as
+                    # unstructured text, and things will work correctly.  But
+                    # we have to strip off any trailing comment on this token
+                    # first, and if it is a quoted string we have to pull out
+                    # the content (we're encoding it, so it no longer needs to
+                    # be quoted).
+                    if part[-1].token_type == 'cfws' and part.comments:
+                        remainder = part.pop(-1)
+                    else:
+                        remainder = ''
+                    for i, token in enumerate(part):
+                        if token.token_type == 'bare-quoted-string':
+                            part[i] = UnstructuredTokenList(token[:])
+                    chunk = get_unstructured(
+                        ''.join(folded.current[last_ew:]+[tstr])).as_encoded_word(charset)
+                    schunk = str(chunk)
+                    lchunk = len(schunk)
+                    if last_ew + lchunk <= folded.maxlen:
+                        del folded.current[last_ew:]
+                        folded.append(schunk)
+                        folded.lastlen = sum(len(x) for x in folded.current)
+                        continue
+                tstr = part.as_encoded_word(charset)
+                tlen = len(tstr)
+                has_ew = True
+            if folded.append_if_fits(part, tstr):
+                if has_ew and not part.comments:
+                    last_ew = len(folded.current) - 1
+                elif part.comments or part.token_type == 'quoted-string':
+                    # If a comment is involved we can't combine EWs.  And if a
+                    # quoted string is involved, it's not worth the effort to
+                    # try to combine them.
+                    last_ew = None
+                continue
+            part._fold(folded)
+
+    def cte_encode(self, charset, policy):
+        res = []
+        last_ew = None
+        is_ew = False
+        for part in self:
+            spart = str(part)
+            try:
+                spart.encode('us-ascii')
+                res.append(spart)
+            except UnicodeEncodeError:
+                is_ew = True
+                if last_ew is None:
+                    if not part.comments:
+                        last_ew = len(res)
+                    res.append(part.cte_encode(charset, policy))
+                elif not part.has_leading_comment():
+                    if part[-1].token_type == 'cfws' and part.comments:
+                        remainder = part.pop(-1)
+                    else:
+                        remainder = ''
+                    for i, token in enumerate(part):
+                        if token.token_type == 'bare-quoted-string':
+                            part[i] = UnstructuredTokenList(token[:])
+                    tl = get_unstructured(''.join(res[last_ew:] + [spart]))
+                    res[last_ew:] = [tl.as_encoded_word(charset)]
+            if part.comments or (not is_ew and part.token_type == 'quoted-string'):
+                last_ew = None
+        return ''.join(res)
+
+class Word(TokenList):
+
+    token_type = 'word'
+
+
+class CFWSList(WhiteSpaceTokenList):
+
+    token_type = 'cfws'
+
+    def has_leading_comment(self):
+        return bool(self.comments)
+
+
+class Atom(TokenList):
+
+    token_type = 'atom'
+
+
+class EncodedWord(TokenList):
+
+    token_type = 'encoded-word'
+    cte = None
+    charset = None
+    lang = None
+
+    @property
+    def encoded(self):
+        if self.cte is not None:
+            return self.cte
+        _ew.encode(str(self), self.charset)
+
+
+
+class QuotedString(TokenList):
+
+    token_type = 'quoted-string'
+
+    @property
+    def content(self):
+        for x in self:
+            if x.token_type == 'bare-quoted-string':
+                return x.value
+
+    @property
+    def quoted_value(self):
+        res = []
+        for x in self:
+            if x.token_type == 'bare-quoted-string':
+                res.append(str(x))
+            else:
+                res.append(x.value)
+        return ''.join(res)
+
+
+class BareQuotedString(QuotedString):
+
+    token_type = 'bare-quoted-string'
+
+    def __str__(self):
+        return quote_string(''.join(self))
+
+    @property
+    def value(self):
+        return ''.join(str(x) for x in self)
+
+
+class Comment(WhiteSpaceTokenList):
+
+    token_type = 'comment'
+
+    def __str__(self):
+        return ''.join(sum([
+                            ["("],
+                            [self.quote(x) for x in self],
+                            [")"],
+                            ], []))
+
+    def quote(self, value):
+        if value.token_type == 'comment':
+            return str(value)
+        return str(value).replace('\\', '\\\\').replace(
+                                  '(', '\(').replace(
+                                  ')', '\)')
+
+    @property
+    def content(self):
+        return ''.join(str(x) for x in self)
+
+    @property
+    def comments(self):
+        return [self.content]
+
+class AddressList(TokenList):
+
+    token_type = 'address-list'
+
+    @property
+    def addresses(self):
+        return [x for x in self if x.token_type=='address']
+
+    @property
+    def mailboxes(self):
+        return sum((x.mailboxes
+                    for x in self if x.token_type=='address'), [])
+
+    @property
+    def all_mailboxes(self):
+        return sum((x.all_mailboxes
+                    for x in self if x.token_type=='address'), [])
+
+
+class Address(TokenList):
+
+    token_type = 'address'
+
+    @property
+    def display_name(self):
+        if self[0].token_type == 'group':
+            return self[0].display_name
+
+    @property
+    def mailboxes(self):
+        if self[0].token_type == 'mailbox':
+            return [self[0]]
+        elif self[0].token_type == 'invalid-mailbox':
+            return []
+        return self[0].mailboxes
+
+    @property
+    def all_mailboxes(self):
+        if self[0].token_type == 'mailbox':
+            return [self[0]]
+        elif self[0].token_type == 'invalid-mailbox':
+            return [self[0]]
+        return self[0].all_mailboxes
+
+class MailboxList(TokenList):
+
+    token_type = 'mailbox-list'
+
+    @property
+    def mailboxes(self):
+        return [x for x in self if x.token_type=='mailbox']
+
+    @property
+    def all_mailboxes(self):
+        return [x for x in self
+            if x.token_type in ('mailbox', 'invalid-mailbox')]
+
+
+class GroupList(TokenList):
+
+    token_type = 'group-list'
+
+    @property
+    def mailboxes(self):
+        if not self or self[0].token_type != 'mailbox-list':
+            return []
+        return self[0].mailboxes
+
+    @property
+    def all_mailboxes(self):
+        if not self or self[0].token_type != 'mailbox-list':
+            return []
+        return self[0].all_mailboxes
+
+
+class Group(TokenList):
+
+    token_type = "group"
+
+    @property
+    def mailboxes(self):
+        if self[2].token_type != 'group-list':
+            return []
+        return self[2].mailboxes
+
+    @property
+    def all_mailboxes(self):
+        if self[2].token_type != 'group-list':
+            return []
+        return self[2].all_mailboxes
+
+    @property
+    def display_name(self):
+        return self[0].display_name
+
+
+class NameAddr(TokenList):
+
+    token_type = 'name-addr'
+
+    @property
+    def display_name(self):
+        if len(self) == 1:
+            return None
+        return self[0].display_name
+
+    @property
+    def local_part(self):
+        return self[-1].local_part
+
+    @property
+    def domain(self):
+        return self[-1].domain
+
+    @property
+    def route(self):
+        return self[-1].route
+
+    @property
+    def addr_spec(self):
+        return self[-1].addr_spec
+
+
+class AngleAddr(TokenList):
+
+    token_type = 'angle-addr'
+
+    @property
+    def local_part(self):
+        for x in self:
+            if x.token_type == 'addr-spec':
+                return x.local_part
+
+    @property
+    def domain(self):
+        for x in self:
+            if x.token_type == 'addr-spec':
+                return x.domain
+
+    @property
+    def route(self):
+        for x in self:
+            if x.token_type == 'obs-route':
+                return x.domains
+
+    @property
+    def addr_spec(self):
+        for x in self:
+            if x.token_type == 'addr-spec':
+                return x.addr_spec
+
+
+class ObsRoute(TokenList):
+
+    token_type = 'obs-route'
+
+    @property
+    def domains(self):
+        return [x.domain for x in self if x.token_type == 'domain']
+
+
+class Mailbox(TokenList):
+
+    token_type = 'mailbox'
+
+    @property
+    def display_name(self):
+        if self[0].token_type == 'name-addr':
+            return self[0].display_name
+
+    @property
+    def local_part(self):
+        return self[0].local_part
+
+    @property
+    def domain(self):
+        return self[0].domain
+
+    @property
+    def route(self):
+        if self[0].token_type == 'name-addr':
+            return self[0].route
+
+    @property
+    def addr_spec(self):
+        return self[0].addr_spec
+
+
+class InvalidMailbox(TokenList):
+
+    token_type = 'invalid-mailbox'
+
+    @property
+    def display_name(self):
+        return None
+
+    local_part = domain = route = addr_spec = display_name
+
+
+class Domain(TokenList):
+
+    token_type = 'domain'
+
+    @property
+    def domain(self):
+        return ''.join(super().value.split())
+
+
+class DotAtom(TokenList):
+
+    token_type = 'dot-atom'
+
+
+class DotAtomText(TokenList):
+
+    token_type = 'dot-atom-text'
+
+
+class AddrSpec(TokenList):
+
+    token_type = 'addr-spec'
+
+    @property
+    def local_part(self):
+        return self[0].local_part
+
+    @property
+    def domain(self):
+        if len(self) < 3:
+            return None
+        return self[-1].domain
+
+    @property
+    def value(self):
+        if len(self) < 3:
+            return self[0].value
+        return self[0].value.rstrip()+self[1].value+self[2].value.lstrip()
+
+    @property
+    def addr_spec(self):
+        nameset = set(self.local_part)
+        if len(nameset) > len(nameset-DOT_ATOM_ENDS):
+            lp = quote_string(self.local_part)
+        else:
+            lp = self.local_part
+        if self.domain is not None:
+            return lp + '@' + self.domain
+        return lp
+
+
+class ObsLocalPart(TokenList):
+
+    token_type = 'obs-local-part'
+
+
+class DisplayName(Phrase):
+
+    token_type = 'display-name'
+
+    @property
+    def display_name(self):
+        res = TokenList(self)
+        if res[0].token_type == 'cfws':
+            res.pop(0)
+        else:
+            if res[0][0].token_type == 'cfws':
+                res[0] = TokenList(res[0][1:])
+        if res[-1].token_type == 'cfws':
+            res.pop()
+        else:
+            if res[-1][-1].token_type == 'cfws':
+                res[-1] = TokenList(res[-1][:-1])
+        return res.value
+
+    @property
+    def value(self):
+        quote = False
+        if self.defects:
+            quote = True
+        else:
+            for x in self:
+                if x.token_type == 'quoted-string':
+                    quote = True
+        if quote:
+            pre = post = ''
+            if self[0].token_type=='cfws' or self[0][0].token_type=='cfws':
+                pre = ' '
+            if self[-1].token_type=='cfws' or self[-1][-1].token_type=='cfws':
+                post = ' '
+            return pre+quote_string(self.display_name)+post
+        else:
+            return super().value
+
+
+class LocalPart(TokenList):
+
+    token_type = 'local-part'
+
+    @property
+    def value(self):
+        if self[0].token_type == "quoted-string":
+            return self[0].quoted_value
+        else:
+            return self[0].value
+
+    @property
+    def local_part(self):
+        # Strip whitespace from front, back, and around dots.
+        res = [DOT]
+        last = DOT
+        last_is_tl = False
+        for tok in self[0] + [DOT]:
+            if tok.token_type == 'cfws':
+                continue
+            if (last_is_tl and tok.token_type == 'dot' and
+                    last[-1].token_type == 'cfws'):
+                res[-1] = TokenList(last[:-1])
+            is_tl = isinstance(tok, TokenList)
+            if (is_tl and last.token_type == 'dot' and
+                    tok[0].token_type == 'cfws'):
+                res.append(TokenList(tok[1:]))
+            else:
+                res.append(tok)
+            last = res[-1]
+            last_is_tl = is_tl
+        res = TokenList(res[1:-1])
+        return res.value
+
+
+class DomainLiteral(TokenList):
+
+    token_type = 'domain-literal'
+
+    @property
+    def domain(self):
+        return ''.join(super().value.split())
+
+    @property
+    def ip(self):
+        for x in self:
+            if x.token_type == 'ptext':
+                return x.value
+
+
+class HeaderLabel(TokenList):
+
+    token_type = 'header-label'
+
+
+class Header(TokenList):
+
+    token_type = 'header'
+
+    def _fold(self, folded):
+        folded.append(str(self.pop(0)))
+        folded.lastlen = len(folded.current[0])
+        # The first line of the header is different from all others: we don't
+        # want to start a new object on a new line if it has any fold points in
+        # it that would allow part of it to be on the first header line.
+        # Further, if the first fold point would fit on the new line, we want
+        # to do that, but if it doesn't we want to put it on the first line.
+        # Folded supports this via the stickyspace attribute.  If this
+        # attribute is not None, it does the special handling.
+        folded.stickyspace = str(self.pop(0)) if self[0].token_type == 'cfws' else ''
+        rest = self.pop(0)
+        if self:
+            raise ValueError("Malformed Header token list")
+        rest._fold(folded)
+
+
+#
+# Terminal classes and instances
+#
+
+class Terminal(str):
+
+    def __new__(cls, value, token_type):
+        self = super().__new__(cls, value)
+        self.token_type = token_type
+        self.defects = []
+        return self
+
+    def __repr__(self):
+        return "{}({})".format(self.__class__.__name__, super().__repr__())
+
+    @property
+    def all_defects(self):
+        return list(self.defects)
+
+    def _pp(self, indent=''):
+        return ["{}{}/{}({}){}".format(
+            indent,
+            self.__class__.__name__,
+            self.token_type,
+            super().__repr__(),
+            '' if not self.defects else ' {}'.format(self.defects),
+            )]
+
+    def cte_encode(self, charset, policy):
+        value = str(self)
+        try:
+            value.encode('us-ascii')
+            return value
+        except UnicodeEncodeError:
+            return _ew.encode(value, charset)
+
+    def pop_trailing_ws(self):
+        # This terminates the recursion.
+        return None
+
+    def pop_leading_fws(self):
+        # This terminates the recursion.
+        return None
+
+    @property
+    def comments(self):
+        return []
+
+    def has_leading_comment(self):
+        return False
+
+    def __getnewargs__(self):
+        return(str(self), self.token_type)
+
+
+class WhiteSpaceTerminal(Terminal):
+
+    @property
+    def value(self):
+        return ' '
+
+    def startswith_fws(self):
+        return True
+
+    has_fws = True
+
+
+class ValueTerminal(Terminal):
+
+    @property
+    def value(self):
+        return self
+
+    def startswith_fws(self):
+        return False
+
+    has_fws = False
+
+    def as_encoded_word(self, charset):
+        return _ew.encode(str(self), charset)
+
+
+class EWWhiteSpaceTerminal(WhiteSpaceTerminal):
+
+    @property
+    def value(self):
+        return ''
+
+    @property
+    def encoded(self):
+        return self[:]
+
+    def __str__(self):
+        return ''
+
+    has_fws = True
+
+
+# XXX these need to become classes and used as instances so
+# that a program can't change them in a parse tree and screw
+# up other parse trees.  Maybe should have  tests for that, too.
+DOT = ValueTerminal('.', 'dot')
+ListSeparator = ValueTerminal(',', 'list-separator')
+RouteComponentMarker = ValueTerminal('@', 'route-component-marker')
+
+#
+# Parser
+#
+
+"""Parse strings according to RFC822/2047/2822/5322 rules.
+
+This is a stateless parser.  Each get_XXX function accepts a string and
+returns either a Terminal or a TokenList representing the RFC object named
+by the method and a string containing the remaining unparsed characters
+from the input.  Thus a parser method consumes the next syntactic construct
+of a given type and returns a token representing the construct plus the
+unparsed remainder of the input string.
+
+For example, if the first element of a structured header is a 'phrase',
+then:
+
+    phrase, value = get_phrase(value)
+
+returns the complete phrase from the start of the string value, plus any
+characters left in the string after the phrase is removed.
+
+"""
+
+_wsp_splitter = re.compile(r'([{}]+)'.format(''.join(WSP))).split
+_non_atom_end_matcher = re.compile(r"[^{}]+".format(
+    ''.join(ATOM_ENDS).replace('\\','\\\\').replace(']','\]'))).match
+_non_printable_finder = re.compile(r"[\x00-\x20\x7F]").findall
+
+def _validate_xtext(xtext):
+    """If input token contains ASCII non-printables, register a defect."""
+
+    non_printables = _non_printable_finder(xtext)
+    if non_printables:
+        xtext.defects.append(errors.NonPrintableDefect(non_printables))
+    if utils._has_surrogates(xtext):
+        xtext.defects.append(errors.UndecodableBytesDefect(
+            "Non-ASCII characters found in header token"))
+
+def _get_ptext_to_endchars(value, endchars):
+    """Scan printables/quoted-pairs until endchars and return unquoted ptext.
+
+    This function turns a run of qcontent, ccontent-without-comments, or
+    dtext-with-quoted-printables into a single string by unquoting any
+    quoted printables.  It returns the string, the remaining value, and
+    a flag that is True iff there were any quoted printables decoded.
+
+    """
+    fragment, *remainder = _wsp_splitter(value, 1)
+    vchars = []
+    escape = False
+    had_qp = False
+    for pos in range(len(fragment)):
+        if fragment[pos] == '\\':
+            if escape:
+                escape = False
+                had_qp = True
+            else:
+                escape = True
+                continue
+        if escape:
+            escape = False
+        elif fragment[pos] in endchars:
+            break
+        vchars.append(fragment[pos])
+    else:
+        pos = pos + 1
+    return ''.join(vchars), ''.join([fragment[pos:]] + remainder), had_qp
+
+def _decode_ew_run(value):
+    """ Decode a run of RFC2047 encoded words.
+
+        _decode_ew_run(value) -> (text, value, defects)
+
+    Scans the supplied value for a run of tokens that look like they are RFC
+    2047 encoded words, decodes those words into text according to RFC 2047
+    rules (whitespace between encoded words is discarded), and returns the text
+    and the remaining value (including any leading whitespace on the remaining
+    value), as well as a list of any defects encountered while decoding.  The
+    input value may not have any leading whitespace.
+
+    """
+    res = []
+    defects = []
+    last_ws = ''
+    while value:
+        try:
+            tok, ws, value = _wsp_splitter(value, 1)
+        except ValueError:
+            tok, ws, value = value, '', ''
+        if not (tok.startswith('=?') and tok.endswith('?=')):
+            return ''.join(res), last_ws + tok + ws + value, defects
+        text, charset, lang, new_defects = _ew.decode(tok)
+        res.append(text)
+        defects.extend(new_defects)
+        last_ws = ws
+    return ''.join(res), last_ws, defects
+
+def get_fws(value):
+    """FWS = 1*WSP
+
+    This isn't the RFC definition.  We're using fws to represent tokens where
+    folding can be done, but when we are parsing the *un*folding has already
+    been done so we don't need to watch out for CRLF.
+
+    """
+    newvalue = value.lstrip()
+    fws = WhiteSpaceTerminal(value[:len(value)-len(newvalue)], 'fws')
+    return fws, newvalue
+
+def get_encoded_word(value):
+    """ encoded-word = "=?" charset "?" encoding "?" encoded-text "?="
+
+    """
+    ew = EncodedWord()
+    if not value.startswith('=?'):
+        raise errors.HeaderParseError(
+            "expected encoded word but found {}".format(value))
+    tok, *remainder = value[2:].split('?=', 1)
+    if tok == value[2:]:
+        raise errors.HeaderParseError(
+            "expected encoded word but found {}".format(value))
+    remstr = ''.join(remainder)
+    if remstr[:2].isdigit():
+        rest, *remainder = remstr.split('?=', 1)
+        tok = tok + '?=' + rest
+    if len(tok.split()) > 1:
+        ew.defects.append(errors.InvalidHeaderDefect(
+            "whitespace inside encoded word"))
+    ew.cte = value
+    value = ''.join(remainder)
+    try:
+        text, charset, lang, defects = _ew.decode('=?' + tok + '?=')
+    except ValueError:
+        raise errors.HeaderParseError(
+            "encoded word format invalid: '{}'".format(ew.cte))
+    ew.charset = charset
+    ew.lang = lang
+    ew.defects.extend(defects)
+    while text:
+        if text[0] in WSP:
+            token, text = get_fws(text)
+            ew.append(token)
+            continue
+        chars, *remainder = _wsp_splitter(text, 1)
+        vtext = ValueTerminal(chars, 'vtext')
+        _validate_xtext(vtext)
+        ew.append(vtext)
+        text = ''.join(remainder)
+    return ew, value
+
+def get_unstructured(value):
+    """unstructured = (*([FWS] vchar) *WSP) / obs-unstruct
+       obs-unstruct = *((*LF *CR *(obs-utext) *LF *CR)) / FWS)
+       obs-utext = %d0 / obs-NO-WS-CTL / LF / CR
+
+       obs-NO-WS-CTL is control characters except WSP/CR/LF.
+
+    So, basically, we have printable runs, plus control characters or nulls in
+    the obsolete syntax, separated by whitespace.  Since RFC 2047 uses the
+    obsolete syntax in its specification, but requires whitespace on either
+    side of the encoded words, I can see no reason to need to separate the
+    non-printable-non-whitespace from the printable runs if they occur, so we
+    parse this into xtext tokens separated by WSP tokens.
+
+    Because an 'unstructured' value must by definition constitute the entire
+    value, this 'get' routine does not return a remaining value, only the
+    parsed TokenList.
+
+    """
+    # XXX: but what about bare CR and LF?  They might signal the start or
+    # end of an encoded word.  YAGNI for now, since out current parsers
+    # will never send us strings with bard CR or LF.
+
+    unstructured = UnstructuredTokenList()
+    while value:
+        if value[0] in WSP:
+            token, value = get_fws(value)
+            unstructured.append(token)
+            continue
+        if value.startswith('=?'):
+            try:
+                token, value = get_encoded_word(value)
+            except errors.HeaderParseError:
+                pass
+            else:
+                have_ws = True
+                if len(unstructured) > 0:
+                    if unstructured[-1].token_type != 'fws':
+                        unstructured.defects.append(errors.InvalidHeaderDefect(
+                            "missing whitespace before encoded word"))
+                        have_ws = False
+                if have_ws and len(unstructured) > 1:
+                    if unstructured[-2].token_type == 'encoded-word':
+                        unstructured[-1] = EWWhiteSpaceTerminal(
+                            unstructured[-1], 'fws')
+                unstructured.append(token)
+                continue
+        tok, *remainder = _wsp_splitter(value, 1)
+        vtext = ValueTerminal(tok, 'vtext')
+        _validate_xtext(vtext)
+        unstructured.append(vtext)
+        value = ''.join(remainder)
+    return unstructured
+
+def get_qp_ctext(value):
+    """ctext = <printable ascii except \ ( )>
+
+    This is not the RFC ctext, since we are handling nested comments in comment
+    and unquoting quoted-pairs here.  We allow anything except the '()'
+    characters, but if we find any ASCII other than the RFC defined printable
+    ASCII an NonPrintableDefect is added to the token's defects list.  Since
+    quoted pairs are converted to their unquoted values, what is returned is
+    a 'ptext' token.  In this case it is a WhiteSpaceTerminal, so it's value
+    is ' '.
+
+    """
+    ptext, value, _ = _get_ptext_to_endchars(value, '()')
+    ptext = WhiteSpaceTerminal(ptext, 'ptext')
+    _validate_xtext(ptext)
+    return ptext, value
+
+def get_qcontent(value):
+    """qcontent = qtext / quoted-pair
+
+    We allow anything except the DQUOTE character, but if we find any ASCII
+    other than the RFC defined printable ASCII an NonPrintableDefect is
+    added to the token's defects list.  Any quoted pairs are converted to their
+    unquoted values, so what is returned is a 'ptext' token.  In this case it
+    is a ValueTerminal.
+
+    """
+    ptext, value, _ = _get_ptext_to_endchars(value, '"')
+    ptext = ValueTerminal(ptext, 'ptext')
+    _validate_xtext(ptext)
+    return ptext, value
+
+def get_atext(value):
+    """atext = <matches _atext_matcher>
+
+    We allow any non-ATOM_ENDS in atext, but add an InvalidATextDefect to
+    the token's defects list if we find non-atext characters.
+    """
+    m = _non_atom_end_matcher(value)
+    if not m:
+        raise errors.HeaderParseError(
+            "expected atext but found '{}'".format(value))
+    atext = m.group()
+    value = value[len(atext):]
+    atext = ValueTerminal(atext, 'atext')
+    _validate_xtext(atext)
+    return atext, value
+
+def get_bare_quoted_string(value):
+    """bare-quoted-string = DQUOTE *([FWS] qcontent) [FWS] DQUOTE
+
+    A quoted-string without the leading or trailing white space.  Its
+    value is the text between the quote marks, with whitespace
+    preserved and quoted pairs decoded.
+    """
+    if value[0] != '"':
+        raise errors.HeaderParseError(
+            "expected '\"' but found '{}'".format(value))
+    bare_quoted_string = BareQuotedString()
+    value = value[1:]
+    while value and value[0] != '"':
+        if value[0] in WSP:
+            token, value = get_fws(value)
+        else:
+            token, value = get_qcontent(value)
+        bare_quoted_string.append(token)
+    if not value:
+        bare_quoted_string.defects.append(errors.InvalidHeaderDefect(
+            "end of header inside quoted string"))
+        return bare_quoted_string, value
+    return bare_quoted_string, value[1:]
+
+def get_comment(value):
+    """comment = "(" *([FWS] ccontent) [FWS] ")"
+       ccontent = ctext / quoted-pair / comment
+
+    We handle nested comments here, and quoted-pair in our qp-ctext routine.
+    """
+    if value and value[0] != '(':
+        raise errors.HeaderParseError(
+            "expected '(' but found '{}'".format(value))
+    comment = Comment()
+    value = value[1:]
+    while value and value[0] != ")":
+        if value[0] in WSP:
+            token, value = get_fws(value)
+        elif value[0] == '(':
+            token, value = get_comment(value)
+        else:
+            token, value = get_qp_ctext(value)
+        comment.append(token)
+    if not value:
+        comment.defects.append(errors.InvalidHeaderDefect(
+            "end of header inside comment"))
+        return comment, value
+    return comment, value[1:]
+
+def get_cfws(value):
+    """CFWS = (1*([FWS] comment) [FWS]) / FWS
+
+    """
+    cfws = CFWSList()
+    while value and value[0] in CFWS_LEADER:
+        if value[0] in WSP:
+            token, value = get_fws(value)
+        else:
+            token, value = get_comment(value)
+        cfws.append(token)
+    return cfws, value
+
+def get_quoted_string(value):
+    """quoted-string = [CFWS] <bare-quoted-string> [CFWS]
+
+    'bare-quoted-string' is an intermediate class defined by this
+    parser and not by the RFC grammar.  It is the quoted string
+    without any attached CFWS.
+    """
+    quoted_string = QuotedString()
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        quoted_string.append(token)
+    token, value = get_bare_quoted_string(value)
+    quoted_string.append(token)
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        quoted_string.append(token)
+    return quoted_string, value
+
+def get_atom(value):
+    """atom = [CFWS] 1*atext [CFWS]
+
+    """
+    atom = Atom()
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        atom.append(token)
+    if value and value[0] in ATOM_ENDS:
+        raise errors.HeaderParseError(
+            "expected atom but found '{}'".format(value))
+    token, value = get_atext(value)
+    atom.append(token)
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        atom.append(token)
+    return atom, value
+
+def get_dot_atom_text(value):
+    """ dot-text = 1*atext *("." 1*atext)
+
+    """
+    dot_atom_text = DotAtomText()
+    if not value or value[0] in ATOM_ENDS:
+        raise errors.HeaderParseError("expected atom at a start of "
+            "dot-atom-text but found '{}'".format(value))
+    while value and value[0] not in ATOM_ENDS:
+        token, value = get_atext(value)
+        dot_atom_text.append(token)
+        if value and value[0] == '.':
+            dot_atom_text.append(DOT)
+            value = value[1:]
+    if dot_atom_text[-1] is DOT:
+        raise errors.HeaderParseError("expected atom at end of dot-atom-text "
+            "but found '{}'".format('.'+value))
+    return dot_atom_text, value
+
+def get_dot_atom(value):
+    """ dot-atom = [CFWS] dot-atom-text [CFWS]
+
+    """
+    dot_atom = DotAtom()
+    if value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        dot_atom.append(token)
+    token, value = get_dot_atom_text(value)
+    dot_atom.append(token)
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        dot_atom.append(token)
+    return dot_atom, value
+
+def get_word(value):
+    """word = atom / quoted-string
+
+    Either atom or quoted-string may start with CFWS.  We have to peel off this
+    CFWS first to determine which type of word to parse.  Afterward we splice
+    the leading CFWS, if any, into the parsed sub-token.
+
+    If neither an atom or a quoted-string is found before the next special, a
+    HeaderParseError is raised.
+
+    The token returned is either an Atom or a QuotedString, as appropriate.
+    This means the 'word' level of the formal grammar is not represented in the
+    parse tree; this is because having that extra layer when manipulating the
+    parse tree is more confusing than it is helpful.
+
+    """
+    if value[0] in CFWS_LEADER:
+        leader, value = get_cfws(value)
+    else:
+        leader = None
+    if value[0]=='"':
+        token, value = get_quoted_string(value)
+    elif value[0] in SPECIALS:
+        raise errors.HeaderParseError("Expected 'atom' or 'quoted-string' "
+                                      "but found '{}'".format(value))
+    else:
+        token, value = get_atom(value)
+    if leader is not None:
+        token[:0] = [leader]
+    return token, value
+
+def get_phrase(value):
+    """ phrase = 1*word / obs-phrase
+        obs-phrase = word *(word / "." / CFWS)
+
+    This means a phrase can be a sequence of words, periods, and CFWS in any
+    order as long as it starts with at least one word.  If anything other than
+    words is detected, an ObsoleteHeaderDefect is added to the token's defect
+    list.  We also accept a phrase that starts with CFWS followed by a dot;
+    this is registered as an InvalidHeaderDefect, since it is not supported by
+    even the obsolete grammar.
+
+    """
+    phrase = Phrase()
+    try:
+        token, value = get_word(value)
+        phrase.append(token)
+    except errors.HeaderParseError:
+        phrase.defects.append(errors.InvalidHeaderDefect(
+            "phrase does not start with word"))
+    while value and value[0] not in PHRASE_ENDS:
+        if value[0]=='.':
+            phrase.append(DOT)
+            phrase.defects.append(errors.ObsoleteHeaderDefect(
+                "period in 'phrase'"))
+            value = value[1:]
+        else:
+            try:
+                token, value = get_word(value)
+            except errors.HeaderParseError:
+                if value[0] in CFWS_LEADER:
+                    token, value = get_cfws(value)
+                    phrase.defects.append(errors.ObsoleteHeaderDefect(
+                        "comment found without atom"))
+                else:
+                    raise
+            phrase.append(token)
+    return phrase, value
+
+def get_local_part(value):
+    """ local-part = dot-atom / quoted-string / obs-local-part
+
+    """
+    local_part = LocalPart()
+    leader = None
+    if value[0] in CFWS_LEADER:
+        leader, value = get_cfws(value)
+    if not value:
+        raise errors.HeaderParseError(
+            "expected local-part but found '{}'".format(value))
+    try:
+        token, value = get_dot_atom(value)
+    except errors.HeaderParseError:
+        try:
+            token, value = get_word(value)
+        except errors.HeaderParseError:
+            if value[0] != '\\' and value[0] in PHRASE_ENDS:
+                raise
+            token = TokenList()
+    if leader is not None:
+        token[:0] = [leader]
+    local_part.append(token)
+    if value and (value[0]=='\\' or value[0] not in PHRASE_ENDS):
+        obs_local_part, value = get_obs_local_part(str(local_part) + value)
+        if obs_local_part.token_type == 'invalid-obs-local-part':
+            local_part.defects.append(errors.InvalidHeaderDefect(
+                "local-part is not dot-atom, quoted-string, or obs-local-part"))
+        else:
+            local_part.defects.append(errors.ObsoleteHeaderDefect(
+                "local-part is not a dot-atom (contains CFWS)"))
+        local_part[0] = obs_local_part
+    try:
+        local_part.value.encode('ascii')
+    except UnicodeEncodeError:
+        local_part.defects.append(errors.NonASCIILocalPartDefect(
+                "local-part contains non-ASCII characters)"))
+    return local_part, value
+
+def get_obs_local_part(value):
+    """ obs-local-part = word *("." word)
+    """
+    obs_local_part = ObsLocalPart()
+    last_non_ws_was_dot = False
+    while value and (value[0]=='\\' or value[0] not in PHRASE_ENDS):
+        if value[0] == '.':
+            if last_non_ws_was_dot:
+                obs_local_part.defects.append(errors.InvalidHeaderDefect(
+                    "invalid repeated '.'"))
+            obs_local_part.append(DOT)
+            last_non_ws_was_dot = True
+            value = value[1:]
+            continue
+        elif value[0]=='\\':
+            obs_local_part.append(ValueTerminal(value[0],
+                                                'misplaced-special'))
+            value = value[1:]
+            obs_local_part.defects.append(errors.InvalidHeaderDefect(
+                "'\\' character outside of quoted-string/ccontent"))
+            last_non_ws_was_dot = False
+            continue
+        if obs_local_part and obs_local_part[-1].token_type != 'dot':
+            obs_local_part.defects.append(errors.InvalidHeaderDefect(
+                "missing '.' between words"))
+        try:
+            token, value = get_word(value)
+            last_non_ws_was_dot = False
+        except errors.HeaderParseError:
+            if value[0] not in CFWS_LEADER:
+                raise
+            token, value = get_cfws(value)
+        obs_local_part.append(token)
+    if (obs_local_part[0].token_type == 'dot' or
+            obs_local_part[0].token_type=='cfws' and
+            obs_local_part[1].token_type=='dot'):
+        obs_local_part.defects.append(errors.InvalidHeaderDefect(
+            "Invalid leading '.' in local part"))
+    if (obs_local_part[-1].token_type == 'dot' or
+            obs_local_part[-1].token_type=='cfws' and
+            obs_local_part[-2].token_type=='dot'):
+        obs_local_part.defects.append(errors.InvalidHeaderDefect(
+            "Invalid trailing '.' in local part"))
+    if obs_local_part.defects:
+        obs_local_part.token_type = 'invalid-obs-local-part'
+    return obs_local_part, value
+
+def get_dtext(value):
+    """ dtext = <printable ascii except \ [ ]> / obs-dtext
+        obs-dtext = obs-NO-WS-CTL / quoted-pair
+
+    We allow anything except the excluded characters, but but if we find any
+    ASCII other than the RFC defined printable ASCII an NonPrintableDefect is
+    added to the token's defects list.  Quoted pairs are converted to their
+    unquoted values, so what is returned is a ptext token, in this case a
+    ValueTerminal.  If there were quoted-printables, an ObsoleteHeaderDefect is
+    added to the returned token's defect list.
+
+    """
+    ptext, value, had_qp = _get_ptext_to_endchars(value, '[]')
+    ptext = ValueTerminal(ptext, 'ptext')
+    if had_qp:
+        ptext.defects.append(errors.ObsoleteHeaderDefect(
+            "quoted printable found in domain-literal"))
+    _validate_xtext(ptext)
+    return ptext, value
+
+def _check_for_early_dl_end(value, domain_literal):
+    if value:
+        return False
+    domain_literal.append(errors.InvalidHeaderDefect(
+        "end of input inside domain-literal"))
+    domain_literal.append(ValueTerminal(']', 'domain-literal-end'))
+    return True
+
+def get_domain_literal(value):
+    """ domain-literal = [CFWS] "[" *([FWS] dtext) [FWS] "]" [CFWS]
+
+    """
+    domain_literal = DomainLiteral()
+    if value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        domain_literal.append(token)
+    if not value:
+        raise errors.HeaderParseError("expected domain-literal")
+    if value[0] != '[':
+        raise errors.HeaderParseError("expected '[' at start of domain-literal "
+                "but found '{}'".format(value))
+    value = value[1:]
+    if _check_for_early_dl_end(value, domain_literal):
+        return domain_literal, value
+    domain_literal.append(ValueTerminal('[', 'domain-literal-start'))
+    if value[0] in WSP:
+        token, value = get_fws(value)
+        domain_literal.append(token)
+    token, value = get_dtext(value)
+    domain_literal.append(token)
+    if _check_for_early_dl_end(value, domain_literal):
+        return domain_literal, value
+    if value[0] in WSP:
+        token, value = get_fws(value)
+        domain_literal.append(token)
+    if _check_for_early_dl_end(value, domain_literal):
+        return domain_literal, value
+    if value[0] != ']':
+        raise errors.HeaderParseError("expected ']' at end of domain-literal "
+                "but found '{}'".format(value))
+    domain_literal.append(ValueTerminal(']', 'domain-literal-end'))
+    value = value[1:]
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        domain_literal.append(token)
+    return domain_literal, value
+
+def get_domain(value):
+    """ domain = dot-atom / domain-literal / obs-domain
+        obs-domain = atom *("." atom))
+
+    """
+    domain = Domain()
+    leader = None
+    if value[0] in CFWS_LEADER:
+        leader, value = get_cfws(value)
+    if not value:
+        raise errors.HeaderParseError(
+            "expected domain but found '{}'".format(value))
+    if value[0] == '[':
+        token, value = get_domain_literal(value)
+        if leader is not None:
+            token[:0] = [leader]
+        domain.append(token)
+        return domain, value
+    try:
+        token, value = get_dot_atom(value)
+    except errors.HeaderParseError:
+        token, value = get_atom(value)
+    if leader is not None:
+        token[:0] = [leader]
+    domain.append(token)
+    if value and value[0] == '.':
+        domain.defects.append(errors.ObsoleteHeaderDefect(
+            "domain is not a dot-atom (contains CFWS)"))
+        if domain[0].token_type == 'dot-atom':
+            domain[:] = domain[0]
+        while value and value[0] == '.':
+            domain.append(DOT)
+            token, value = get_atom(value[1:])
+            domain.append(token)
+    return domain, value
+
+def get_addr_spec(value):
+    """ addr-spec = local-part "@" domain
+
+    """
+    addr_spec = AddrSpec()
+    token, value = get_local_part(value)
+    addr_spec.append(token)
+    if not value or value[0] != '@':
+        addr_spec.defects.append(errors.InvalidHeaderDefect(
+            "add-spec local part with no domain"))
+        return addr_spec, value
+    addr_spec.append(ValueTerminal('@', 'address-at-symbol'))
+    token, value = get_domain(value[1:])
+    addr_spec.append(token)
+    return addr_spec, value
+
+def get_obs_route(value):
+    """ obs-route = obs-domain-list ":"
+        obs-domain-list = *(CFWS / ",") "@" domain *("," [CFWS] ["@" domain])
+
+        Returns an obs-route token with the appropriate sub-tokens (that is,
+        there is no obs-domain-list in the parse tree).
+    """
+    obs_route = ObsRoute()
+    while value and (value[0]==',' or value[0] in CFWS_LEADER):
+        if value[0] in CFWS_LEADER:
+            token, value = get_cfws(value)
+            obs_route.append(token)
+        elif value[0] == ',':
+            obs_route.append(ListSeparator)
+            value = value[1:]
+    if not value or value[0] != '@':
+        raise errors.HeaderParseError(
+            "expected obs-route domain but found '{}'".format(value))
+    obs_route.append(RouteComponentMarker)
+    token, value = get_domain(value[1:])
+    obs_route.append(token)
+    while value and value[0]==',':
+        obs_route.append(ListSeparator)
+        value = value[1:]
+        if not value:
+            break
+        if value[0] in CFWS_LEADER:
+            token, value = get_cfws(value)
+            obs_route.append(token)
+        if value[0] == '@':
+            obs_route.append(RouteComponentMarker)
+            token, value = get_domain(value[1:])
+            obs_route.append(token)
+    if not value:
+        raise errors.HeaderParseError("end of header while parsing obs-route")
+    if value[0] != ':':
+        raise errors.HeaderParseError( "expected ':' marking end of "
+            "obs-route but found '{}'".format(value))
+    obs_route.append(ValueTerminal(':', 'end-of-obs-route-marker'))
+    return obs_route, value[1:]
+
+def get_angle_addr(value):
+    """ angle-addr = [CFWS] "<" addr-spec ">" [CFWS] / obs-angle-addr
+        obs-angle-addr = [CFWS] "<" obs-route addr-spec ">" [CFWS]
+
+    """
+    angle_addr = AngleAddr()
+    if value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        angle_addr.append(token)
+    if not value or value[0] != '<':
+        raise errors.HeaderParseError(
+            "expected angle-addr but found '{}'".format(value))
+    angle_addr.append(ValueTerminal('<', 'angle-addr-start'))
+    value = value[1:]
+    try:
+        token, value = get_addr_spec(value)
+    except errors.HeaderParseError:
+        try:
+            token, value = get_obs_route(value)
+            angle_addr.defects.append(errors.ObsoleteHeaderDefect(
+                "obsolete route specification in angle-addr"))
+        except errors.HeaderParseError:
+            raise errors.HeaderParseError(
+                "expected addr-spec or but found '{}'".format(value))
+        angle_addr.append(token)
+        token, value = get_addr_spec(value)
+    angle_addr.append(token)
+    if value and value[0] == '>':
+        value = value[1:]
+    else:
+        angle_addr.defects.append(errors.InvalidHeaderDefect(
+            "missing trailing '>' on angle-addr"))
+    angle_addr.append(ValueTerminal('>', 'angle-addr-end'))
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        angle_addr.append(token)
+    return angle_addr, value
+
+def get_display_name(value):
+    """ display-name = phrase
+
+    Because this is simply a name-rule, we don't return a display-name
+    token containing a phrase, but rather a display-name token with
+    the content of the phrase.
+
+    """
+    display_name = DisplayName()
+    token, value = get_phrase(value)
+    display_name.extend(token[:])
+    display_name.defects = token.defects[:]
+    return display_name, value
+
+
+def get_name_addr(value):
+    """ name-addr = [display-name] angle-addr
+
+    """
+    name_addr = NameAddr()
+    # Both the optional display name and the angle-addr can start with cfws.
+    leader = None
+    if value[0] in CFWS_LEADER:
+        leader, value = get_cfws(value)
+        if not value:
+            raise errors.HeaderParseError(
+                "expected name-addr but found '{}'".format(leader))
+    if value[0] != '<':
+        if value[0] in PHRASE_ENDS:
+            raise errors.HeaderParseError(
+                "expected name-addr but found '{}'".format(value))
+        token, value = get_display_name(value)
+        if not value:
+            raise errors.HeaderParseError(
+                "expected name-addr but found '{}'".format(token))
+        if leader is not None:
+            token[0][:0] = [leader]
+            leader = None
+        name_addr.append(token)
+    token, value = get_angle_addr(value)
+    if leader is not None:
+        token[:0] = [leader]
+    name_addr.append(token)
+    return name_addr, value
+
+def get_mailbox(value):
+    """ mailbox = name-addr / addr-spec
+
+    """
+    # The only way to figure out if we are dealing with a name-addr or an
+    # addr-spec is to try parsing each one.
+    mailbox = Mailbox()
+    try:
+        token, value = get_name_addr(value)
+    except errors.HeaderParseError:
+        try:
+            token, value = get_addr_spec(value)
+        except errors.HeaderParseError:
+            raise errors.HeaderParseError(
+                "expected mailbox but found '{}'".format(value))
+    if any(isinstance(x, errors.InvalidHeaderDefect)
+                       for x in token.all_defects):
+        mailbox.token_type = 'invalid-mailbox'
+    mailbox.append(token)
+    return mailbox, value
+
+def get_invalid_mailbox(value, endchars):
+    """ Read everything up to one of the chars in endchars.
+
+    This is outside the formal grammar.  The InvalidMailbox TokenList that is
+    returned acts like a Mailbox, but the data attributes are None.
+
+    """
+    invalid_mailbox = InvalidMailbox()
+    while value and value[0] not in endchars:
+        if value[0] in PHRASE_ENDS:
+            invalid_mailbox.append(ValueTerminal(value[0],
+                                                 'misplaced-special'))
+            value = value[1:]
+        else:
+            token, value = get_phrase(value)
+            invalid_mailbox.append(token)
+    return invalid_mailbox, value
+
+def get_mailbox_list(value):
+    """ mailbox-list = (mailbox *("," mailbox)) / obs-mbox-list
+        obs-mbox-list = *([CFWS] ",") mailbox *("," [mailbox / CFWS])
+
+    For this routine we go outside the formal grammar in order to improve error
+    handling.  We recognize the end of the mailbox list only at the end of the
+    value or at a ';' (the group terminator).  This is so that we can turn
+    invalid mailboxes into InvalidMailbox tokens and continue parsing any
+    remaining valid mailboxes.  We also allow all mailbox entries to be null,
+    and this condition is handled appropriately at a higher level.
+
+    """
+    mailbox_list = MailboxList()
+    while value and value[0] != ';':
+        try:
+            token, value = get_mailbox(value)
+            mailbox_list.append(token)
+        except errors.HeaderParseError:
+            leader = None
+            if value[0] in CFWS_LEADER:
+                leader, value = get_cfws(value)
+                if not value or value[0] in ',;':
+                    mailbox_list.append(leader)
+                    mailbox_list.defects.append(errors.ObsoleteHeaderDefect(
+                        "empty element in mailbox-list"))
+                else:
+                    token, value = get_invalid_mailbox(value, ',;')
+                    if leader is not None:
+                        token[:0] = [leader]
+                    mailbox_list.append(token)
+                    mailbox_list.defects.append(errors.InvalidHeaderDefect(
+                        "invalid mailbox in mailbox-list"))
+            elif value[0] == ',':
+                mailbox_list.defects.append(errors.ObsoleteHeaderDefect(
+                    "empty element in mailbox-list"))
+            else:
+                token, value = get_invalid_mailbox(value, ',;')
+                if leader is not None:
+                    token[:0] = [leader]
+                mailbox_list.append(token)
+                mailbox_list.defects.append(errors.InvalidHeaderDefect(
+                    "invalid mailbox in mailbox-list"))
+        if value and value[0] not in ',;':
+            # Crap after mailbox; treat it as an invalid mailbox.
+            # The mailbox info will still be available.
+            mailbox = mailbox_list[-1]
+            mailbox.token_type = 'invalid-mailbox'
+            token, value = get_invalid_mailbox(value, ',;')
+            mailbox.extend(token)
+            mailbox_list.defects.append(errors.InvalidHeaderDefect(
+                "invalid mailbox in mailbox-list"))
+        if value and value[0] == ',':
+            mailbox_list.append(ListSeparator)
+            value = value[1:]
+    return mailbox_list, value
+
+
+def get_group_list(value):
+    """ group-list = mailbox-list / CFWS / obs-group-list
+        obs-group-list = 1*([CFWS] ",") [CFWS]
+
+    """
+    group_list = GroupList()
+    if not value:
+        group_list.defects.append(errors.InvalidHeaderDefect(
+            "end of header before group-list"))
+        return group_list, value
+    leader = None
+    if value and value[0] in CFWS_LEADER:
+        leader, value = get_cfws(value)
+        if not value:
+            # This should never happen in email parsing, since CFWS-only is a
+            # legal alternative to group-list in a group, which is the only
+            # place group-list appears.
+            group_list.defects.append(errors.InvalidHeaderDefect(
+                "end of header in group-list"))
+            group_list.append(leader)
+            return group_list, value
+        if value[0] == ';':
+            group_list.append(leader)
+            return group_list, value
+    token, value = get_mailbox_list(value)
+    if len(token.all_mailboxes)==0:
+        if leader is not None:
+            group_list.append(leader)
+        group_list.extend(token)
+        group_list.defects.append(errors.ObsoleteHeaderDefect(
+            "group-list with empty entries"))
+        return group_list, value
+    if leader is not None:
+        token[:0] = [leader]
+    group_list.append(token)
+    return group_list, value
+
+def get_group(value):
+    """ group = display-name ":" [group-list] ";" [CFWS]
+
+    """
+    group = Group()
+    token, value = get_display_name(value)
+    if not value or value[0] != ':':
+        raise errors.HeaderParseError("expected ':' at end of group "
+            "display name but found '{}'".format(value))
+    group.append(token)
+    group.append(ValueTerminal(':', 'group-display-name-terminator'))
+    value = value[1:]
+    if value and value[0] == ';':
+        group.append(ValueTerminal(';', 'group-terminator'))
+        return group, value[1:]
+    token, value = get_group_list(value)
+    group.append(token)
+    if not value:
+        group.defects.append(errors.InvalidHeaderDefect(
+            "end of header in group"))
+    if value[0] != ';':
+        raise errors.HeaderParseError(
+            "expected ';' at end of group but found {}".format(value))
+    group.append(ValueTerminal(';', 'group-terminator'))
+    value = value[1:]
+    if value and value[0] in CFWS_LEADER:
+        token, value = get_cfws(value)
+        group.append(token)
+    return group, value
+
+def get_address(value):
+    """ address = mailbox / group
+
+    Note that counter-intuitively, an address can be either a single address or
+    a list of addresses (a group).  This is why the returned Address object has
+    a 'mailboxes' attribute which treats a single address as a list of length
+    one.  When you need to differentiate between to two cases, extract the single
+    element, which is either a mailbox or a group token.
+
+    """
+    # The formal grammar isn't very helpful when parsing an address.  mailbox
+    # and group, especially when allowing for obsolete forms, start off very
+    # similarly.  It is only when you reach one of @, <, or : that you know
+    # what you've got.  So, we try each one in turn, starting with the more
+    # likely of the two.  We could perhaps make this more efficient by looking
+    # for a phrase and then branching based on the next character, but that
+    # would be a premature optimization.
+    address = Address()
+    try:
+        token, value = get_group(value)
+    except errors.HeaderParseError:
+        try:
+            token, value = get_mailbox(value)
+        except errors.HeaderParseError:
+            raise errors.HeaderParseError(
+                "expected address but found '{}'".format(value))
+    address.append(token)
+    return address, value
+
+def get_address_list(value):
+    """ address_list = (address *("," address)) / obs-addr-list
+        obs-addr-list = *([CFWS] ",") address *("," [address / CFWS])
+
+    We depart from the formal grammar here by continuing to parse until the end
+    of the input, assuming the input to be entirely composed of an
+    address-list.  This is always true in email parsing, and allows us
+    to skip invalid addresses to parse additional valid ones.
+
+    """
+    address_list = AddressList()
+    while value:
+        try:
+            token, value = get_address(value)
+            address_list.append(token)
+        except errors.HeaderParseError as err:
+            leader = None
+            if value[0] in CFWS_LEADER:
+                leader, value = get_cfws(value)
+                if not value or value[0] == ',':
+                    address_list.append(leader)
+                    address_list.defects.append(errors.ObsoleteHeaderDefect(
+                        "address-list entry with no content"))
+                else:
+                    token, value = get_invalid_mailbox(value, ',')
+                    if leader is not None:
+                        token[:0] = [leader]
+                    address_list.append(Address([token]))
+                    address_list.defects.append(errors.InvalidHeaderDefect(
+                        "invalid address in address-list"))
+            elif value[0] == ',':
+                address_list.defects.append(errors.ObsoleteHeaderDefect(
+                    "empty element in address-list"))
+            else:
+                token, value = get_invalid_mailbox(value, ',')
+                if leader is not None:
+                    token[:0] = [leader]
+                address_list.append(Address([token]))
+                address_list.defects.append(errors.InvalidHeaderDefect(
+                    "invalid address in address-list"))
+        if value and value[0] != ',':
+            # Crap after address; treat it as an invalid mailbox.
+            # The mailbox info will still be available.
+            mailbox = address_list[-1][0]
+            mailbox.token_type = 'invalid-mailbox'
+            token, value = get_invalid_mailbox(value, ',')
+            mailbox.extend(token)
+            address_list.defects.append(errors.InvalidHeaderDefect(
+                "invalid address in address-list"))
+        if value:  # Must be a , at this point.
+            address_list.append(ValueTerminal(',', 'list-separator'))
+            value = value[1:]
+    return address_list, value
diff --git a/Lib/email/_headerregistry.py b/Lib/email/_headerregistry.py
new file mode 100644
index 0000000..6588546
--- /dev/null
+++ b/Lib/email/_headerregistry.py
@@ -0,0 +1,456 @@
+"""Representing and manipulating email headers via custom objects.
+
+This module provides an implementation of the HeaderRegistry API.
+The implementation is designed to flexibly follow RFC5322 rules.
+
+Eventually HeaderRegistry will be a public API, but it isn't yet,
+and will probably change some before that happens.
+
+"""
+
+from email import utils
+from email import errors
+from email import _header_value_parser as parser
+
+class Address:
+
+    def __init__(self, display_name='', username='', domain='', addr_spec=None):
+        """Create an object represeting a full email address.
+
+        An address can have a 'display_name', a 'username', and a 'domain'.  In
+        addition to specifying the username and domain separately, they may be
+        specified together by using the addr_spec keyword *instead of* the
+        username and domain keywords.  If an addr_spec string is specified it
+        must be properly quoted according to RFC 5322 rules; an error will be
+        raised if it is not.
+
+        An Address object has display_name, username, domain, and addr_spec
+        attributes, all of which are read-only.  The addr_spec and the string
+        value of the object are both quoted according to RFC5322 rules, but
+        without any Content Transfer Encoding.
+
+        """
+        # This clause with its potential 'raise' may only happen when an
+        # application program creates an Address object using an addr_spec
+        # keyword.  The email library code itself must always supply username
+        # and domain.
+        if addr_spec is not None:
+            if username or domain:
+                raise TypeError("addrspec specified when username and/or "
+                                "domain also specified")
+            a_s, rest = parser.get_addr_spec(addr_spec)
+            if rest:
+                raise ValueError("Invalid addr_spec; only '{}' "
+                                 "could be parsed from '{}'".format(
+                                    a_s, addr_spec))
+            if a_s.all_defects:
+                raise a_s.all_defects[0]
+            username = a_s.local_part
+            domain = a_s.domain
+        self._display_name = display_name
+        self._username = username
+        self._domain = domain
+
+    @property
+    def display_name(self):
+        return self._display_name
+
+    @property
+    def username(self):
+        return self._username
+
+    @property
+    def domain(self):
+        return self._domain
+
+    @property
+    def addr_spec(self):
+        """The addr_spec (username@domain) portion of the address, quoted
+        according to RFC 5322 rules, but with no Content Transfer Encoding.
+        """
+        nameset = set(self.username)
+        if len(nameset) > len(nameset-parser.DOT_ATOM_ENDS):
+            lp = parser.quote_string(self.username)
+        else:
+            lp = self.username
+        if self.domain:
+            return lp + '@' + self.domain
+        if not lp:
+            return '<>'
+        return lp
+
+    def __repr__(self):
+        return "Address(display_name={!r}, username={!r}, domain={!r})".format(
+                        self.display_name, self.username, self.domain)
+
+    def __str__(self):
+        nameset = set(self.display_name)
+        if len(nameset) > len(nameset-parser.SPECIALS):
+            disp = parser.quote_string(self.display_name)
+        else:
+            disp = self.display_name
+        if disp:
+            addr_spec = '' if self.addr_spec=='<>' else self.addr_spec
+            return "{} <{}>".format(disp, addr_spec)
+        return self.addr_spec
+
+    def __eq__(self, other):
+        if type(other) != type(self):
+            return False
+        return (self.display_name == other.display_name and
+                self.username == other.username and
+                self.domain == other.domain)
+
+
+class Group:
+
+    def __init__(self, display_name=None, addresses=None):
+        """Create an object representing an address group.
+
+        An address group consists of a display_name followed by colon and an
+        list of addresses (see Address) terminated by a semi-colon.  The Group
+        is created by specifying a display_name and a possibly empty list of
+        Address objects.  A Group can also be used to represent a single
+        address that is not in a group, which is convenient when manipulating
+        lists that are a combination of Groups and individual Addresses.  In
+        this case the display_name should be set to None.  In particular, the
+        string representation of a Group whose display_name is None is the same
+        as the Address object, if there is one and only one Address object in
+        the addresses list.
+
+        """
+        self._display_name = display_name
+        self._addresses = tuple(addresses) if addresses else tuple()
+
+    @property
+    def display_name(self):
+        return self._display_name
+
+    @property
+    def addresses(self):
+        return self._addresses
+
+    def __repr__(self):
+        return "Group(display_name={!r}, addresses={!r}".format(
+                 self.display_name, self.addresses)
+
+    def __str__(self):
+        if self.display_name is None and len(self.addresses)==1:
+            return str(self.addresses[0])
+        disp = self.display_name
+        if disp is not None:
+            nameset = set(disp)
+            if len(nameset) > len(nameset-parser.SPECIALS):
+                disp = parser.quote_string(disp)
+        adrstr = ", ".join(str(x) for x in self.addresses)
+        adrstr = ' ' + adrstr if adrstr else adrstr
+        return "{}:{};".format(disp, adrstr)
+
+    def __eq__(self, other):
+        if type(other) != type(self):
+            return False
+        return (self.display_name == other.display_name and
+                self.addresses == other.addresses)
+
+
+# Header Classes #
+
+class BaseHeader(str):
+
+    """Base class for message headers.
+
+    Implements generic behavior and provides tools for subclasses.
+
+    A subclass must define a classmethod named 'parse' that takes an unfolded
+    value string and a dictionary as its arguments.  The dictionary will
+    contain one key, 'defects', initialized to an empty list.  After the call
+    the dictionary must contain two additional keys: parse_tree, set to the
+    parse tree obtained from parsing the header, and 'decoded', set to the
+    string value of the idealized representation of the data from the value.
+    (That is, encoded words are decoded, and values that have canonical
+    representations are so represented.)
+
+    The defects key is intended to collect parsing defects, which the message
+    parser will subsequently dispose of as appropriate.  The parser should not,
+    insofar as practical, raise any errors.  Defects should be added to the
+    list instead.  The standard header parsers register defects for RFC
+    compliance issues, for obsolete RFC syntax, and for unrecoverable parsing
+    errors.
+
+    The parse method may add additional keys to the dictionary.  In this case
+    the subclass must define an 'init' method, which will be passed the
+    dictionary as its keyword arguments.  The method should use (usually by
+    setting them as the value of similarly named attributes) and remove all the
+    extra keys added by its parse method, and then use super to call its parent
+    class with the remaining arguments and keywords.
+
+    The subclass should also make sure that a 'max_count' attribute is defined
+    that is either None or 1. XXX: need to better define this API.
+
+    """
+
+    def __new__(cls, name, value):
+        kwds = {'defects': []}
+        cls.parse(value, kwds)
+        if utils._has_surrogates(kwds['decoded']):
+            kwds['decoded'] = utils._sanitize(kwds['decoded'])
+        self = str.__new__(cls, kwds['decoded'])
+        del kwds['decoded']
+        self.init(name, **kwds)
+        return self
+
+    def init(self, name, *, parse_tree, defects):
+        self._name = name
+        self._parse_tree = parse_tree
+        self._defects = defects
+
+    @property
+    def name(self):
+        return self._name
+
+    @property
+    def defects(self):
+        return tuple(self._defects)
+
+    def __reduce__(self):
+        return (
+            _reconstruct_header,
+            (
+                self.__class__.__name__,
+                self.__class__.__bases__,
+                str(self),
+            ),
+            self.__dict__)
+
+    @classmethod
+    def _reconstruct(cls, value):
+        return str.__new__(cls, value)
+
+    def fold(self, *, policy):
+        """Fold header according to policy.
+
+        The parsed representation of the header is folded according to
+        RFC5322 rules, as modified by the policy.  If the parse tree
+        contains surrogateescaped bytes, the bytes are CTE encoded using
+        the charset 'unknown-8bit".
+
+        Any non-ASCII characters in the parse tree are CTE encoded using
+        charset utf-8. XXX: make this a policy setting.
+
+        The returned value is an ASCII-only string possibly containing linesep
+        characters, and ending with a linesep character.  The string includes
+        the header name and the ': ' separator.
+
+        """
+        # At some point we need to only put fws here if it was in the source.
+        header = parser.Header([
+            parser.HeaderLabel([
+                parser.ValueTerminal(self.name, 'header-name'),
+                parser.ValueTerminal(':', 'header-sep')]),
+            parser.CFWSList([parser.WhiteSpaceTerminal(' ', 'fws')]),
+                             self._parse_tree])
+        return header.fold(policy=policy)
+
+
+def _reconstruct_header(cls_name, bases, value):
+    return type(cls_name, bases, {})._reconstruct(value)
+
+
+class UnstructuredHeader:
+
+    max_count = None
+    value_parser = staticmethod(parser.get_unstructured)
+
+    @classmethod
+    def parse(cls, value, kwds):
+        kwds['parse_tree'] = cls.value_parser(value)
+        kwds['decoded'] = str(kwds['parse_tree'])
+
+
+class UniqueUnstructuredHeader(UnstructuredHeader):
+
+    max_count = 1
+
+
+class DateHeader:
+
+    """Header whose value consists of a single timestamp.
+
+    Provides an additional attribute, datetime, which is either an aware
+    datetime using a timezone, or a naive datetime if the timezone
+    in the input string is -0000.  Also accepts a datetime as input.
+    The 'value' attribute is the normalized form of the timestamp,
+    which means it is the output of format_datetime on the datetime.
+    """
+
+    max_count = None
+
+    # This is used only for folding, not for creating 'decoded'.
+    value_parser = staticmethod(parser.get_unstructured)
+
+    @classmethod
+    def parse(cls, value, kwds):
+        if not value:
+            kwds['defects'].append(errors.HeaderMissingRequiredValue())
+            kwds['datetime'] = None
+            kwds['decoded'] = ''
+            kwds['parse_tree'] = parser.TokenList()
+            return
+        if isinstance(value, str):
+            value = utils.parsedate_to_datetime(value)
+        kwds['datetime'] = value
+        kwds['decoded'] = utils.format_datetime(kwds['datetime'])
+        kwds['parse_tree'] = cls.value_parser(kwds['decoded'])
+
+    def init(self, *args, **kw):
+        self._datetime = kw.pop('datetime')
+        super().init(*args, **kw)
+
+    @property
+    def datetime(self):
+        return self._datetime
+
+
+class UniqueDateHeader(DateHeader):
+
+    max_count = 1
+
+
+class AddressHeader:
+
+    max_count = None
+
+    @staticmethod
+    def value_parser(value):
+        address_list, value = parser.get_address_list(value)
+        assert not value, 'this should not happen'
+        return address_list
+
+    @classmethod
+    def parse(cls, value, kwds):
+        if isinstance(value, str):
+            # We are translating here from the RFC language (address/mailbox)
+            # to our API language (group/address).
+            kwds['parse_tree'] = address_list = cls.value_parser(value)
+            groups = []
+            for addr in address_list.addresses:
+                groups.append(Group(addr.display_name,
+                                    [Address(mb.display_name or '',
+                                             mb.local_part or '',
+                                             mb.domain or '')
+                                     for mb in addr.all_mailboxes]))
+            defects = list(address_list.all_defects)
+        else:
+            # Assume it is Address/Group stuff
+            if not hasattr(value, '__iter__'):
+                value = [value]
+            groups = [Group(None, [item]) if not hasattr(item, 'addresses')
+                                          else item
+                                    for item in value]
+            defects = []
+        kwds['groups'] = groups
+        kwds['defects'] = defects
+        kwds['decoded'] = ', '.join([str(item) for item in groups])
+        if 'parse_tree' not in kwds:
+            kwds['parse_tree'] = cls.value_parser(kwds['decoded'])
+
+    def init(self, *args, **kw):
+        self._groups = tuple(kw.pop('groups'))
+        self._addresses = None
+        super().init(*args, **kw)
+
+    @property
+    def groups(self):
+        return self._groups
+
+    @property
+    def addresses(self):
+        if self._addresses is None:
+            self._addresses = tuple([address for group in self._groups
+                                             for address in group.addresses])
+        return self._addresses
+
+
+class UniqueAddressHeader(AddressHeader):
+
+    max_count = 1
+
+
+class SingleAddressHeader(AddressHeader):
+
+    @property
+    def address(self):
+        if len(self.addresses)!=1:
+            raise ValueError(("value of single address header {} is not "
+                "a single address").format(self.name))
+        return self.addresses[0]
+
+
+class UniqueSingleAddressHeader(SingleAddressHeader):
+
+    max_count = 1
+
+
+# The header factory #
+
+_default_header_map = {
+    'subject':          UniqueUnstructuredHeader,
+    'date':             UniqueDateHeader,
+    'resent-date':      DateHeader,
+    'orig-date':        UniqueDateHeader,
+    'sender':           UniqueSingleAddressHeader,
+    'resent-sender':    SingleAddressHeader,
+    'to':               UniqueAddressHeader,
+    'resent-to':        AddressHeader,
+    'cc':               UniqueAddressHeader,
+    'resent-cc':        AddressHeader,
+    'bcc':              UniqueAddressHeader,
+    'resent-bcc':       AddressHeader,
+    'from':             UniqueAddressHeader,
+    'resent-from':      AddressHeader,
+    'reply-to':         UniqueAddressHeader,
+    }
+
+class HeaderRegistry:
+
+    """A header_factory and header registry."""
+
+    def __init__(self, base_class=BaseHeader, default_class=UnstructuredHeader,
+                       use_default_map=True):
+        """Create a header_factory that works with the Policy API.
+
+        base_class is the class that will be the last class in the created
+        header class's __bases__ list.  default_class is the class that will be
+        used if "name" (see __call__) does not appear in the registry.
+        use_default_map controls whether or not the default mapping of names to
+        specialized classes is copied in to the registry when the factory is
+        created.  The default is True.
+
+        """
+        self.registry = {}
+        self.base_class = base_class
+        self.default_class = default_class
+        if use_default_map:
+            self.registry.update(_default_header_map)
+
+    def map_to_type(self, name, cls):
+        """Register cls as the specialized class for handling "name" headers.
+
+        """
+        self.registry[name.lower()] = cls
+
+    def __getitem__(self, name):
+        cls = self.registry.get(name.lower(), self.default_class)
+        return type('_'+cls.__name__, (cls, self.base_class), {})
+
+    def __call__(self, name, value):
+        """Create a header instance for header 'name' from 'value'.
+
+        Creates a header instance by creating a specialized class for parsing
+        and representing the specified header by combining the factory
+        base_class with a specialized class from the registry or the
+        default_class, and passing the name and value to the constructed
+        class's constructor.
+
+        """
+        return self[name](name, value)
diff --git a/Lib/email/_policybase.py b/Lib/email/_policybase.py
index 05736d0..6bc298b 100644
--- a/Lib/email/_policybase.py
+++ b/Lib/email/_policybase.py
@@ -64,10 +64,16 @@ class _PolicyBase:
         except for the changes passed in as keyword arguments.
 
         """
+        newpolicy = self.__class__.__new__(self.__class__)
         for attr, value in self.__dict__.items():
-            if attr not in kw:
-                kw[attr] = value
-        return self.__class__(**kw)
+            object.__setattr__(newpolicy, attr, value)
+        for attr, value in kw.items():
+            if not hasattr(self, attr):
+                raise TypeError(
+                    "{!r} is an invalid keyword argument for {}".format(
+                        attr, self.__class__.__name__))
+            object.__setattr__(newpolicy, attr, value)
+        return newpolicy
 
     def __setattr__(self, name, value):
         if hasattr(self, name):
diff --git a/Lib/email/errors.py b/Lib/email/errors.py
index c04deb4..f916229 100644
--- a/Lib/email/errors.py
+++ b/Lib/email/errors.py
@@ -5,7 +5,6 @@
 """email package exception classes."""
 
 
-
 class MessageError(Exception):
     """Base class for errors in the email package."""
 
@@ -30,9 +29,8 @@ class CharsetError(MessageError):
     """An illegal charset was given."""
 
 
-
 # These are parsing defects which the parser was able to work around.
-class MessageDefect(Exception):
+class MessageDefect(ValueError):
     """Base class for a message defect."""
 
     def __init__(self, line=None):
@@ -58,3 +56,42 @@ class MultipartInvariantViolationDefect(MessageDefect):
 
 class InvalidMultipartContentTransferEncodingDefect(MessageDefect):
     """An invalid content transfer encoding was set on the multipart itself."""
+
+class UndecodableBytesDefect(MessageDefect):
+    """Header contained bytes that could not be decoded"""
+
+class InvalidBase64PaddingDefect(MessageDefect):
+    """base64 encoded sequence had an incorrect length"""
+
+class InvalidBase64CharactersDefect(MessageDefect):
+    """base64 encoded sequence had characters not in base64 alphabet"""
+
+# These errors are specific to header parsing.
+
+class HeaderDefect(MessageDefect):
+    """Base class for a header defect."""
+
+class InvalidHeaderDefect(HeaderDefect):
+    """Header is not valid, message gives details."""
+
+class HeaderMissingRequiredValue(HeaderDefect):
+    """A header that must have a value had none"""
+
+class NonPrintableDefect(HeaderDefect):
+    """ASCII characters outside the ascii-printable range found"""
+
+    def __init__(self, non_printables):
+        super().__init__(non_printables)
+        self.non_printables = non_printables
+
+    def __str__(self):
+        return ("the following ASCII non-printables found in header: "
+            "{}".format(self.non_printables))
+
+class ObsoleteHeaderDefect(HeaderDefect):
+    """Header uses syntax declared obsolete by RFC 5322"""
+
+class NonASCIILocalPartDefect(HeaderDefect):
+    """local_part contains non-ASCII characters"""
+    # This defect only occurs during unicode parsing, not when
+    # parsing messages decoded from binary.
diff --git a/Lib/email/generator.py b/Lib/email/generator.py
index bfa288b..fcecf93 100644
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -95,9 +95,15 @@ class Generator:
         self._encoded_NL = self._encode(self._NL)
         self._EMPTY = ''
         self._encoded_EMTPY = self._encode('')
-        p = self.policy
+        # Because we use clone (below) when we recursively process message
+        # subparts, and because clone uses the computed policy (not None),
+        # submessages will automatically get set to the computed policy when
+        # they are processed by this code.
+        old_gen_policy = self.policy
+        old_msg_policy = msg.policy
         try:
             self.policy = policy
+            msg.policy = policy
             if unixfrom:
                 ufrom = msg.get_unixfrom()
                 if not ufrom:
@@ -105,7 +111,8 @@ class Generator:
                 self.write(ufrom + self._NL)
             self._write(msg)
         finally:
-            self.policy = p
+            self.policy = old_gen_policy
+            msg.policy = old_msg_policy
 
     def clone(self, fp):
         """Clone this generator with the exact same options."""
diff --git a/Lib/email/policy.py b/Lib/email/policy.py
index dae2dc7..ea90a8f 100644
--- a/Lib/email/policy.py
+++ b/Lib/email/policy.py
@@ -2,11 +2,178 @@
 code that adds all the email6 features.
 """
 
-from email._policybase import Policy, compat32, Compat32
+from email._policybase import Policy, Compat32, compat32
+from email.utils import _has_surrogates
+from email._headerregistry import HeaderRegistry as _HeaderRegistry
 
-# XXX: temporarily derive everything from compat32.
+__all__ = [
+    'Compat32',
+    'compat32',
+    'Policy',
+    'EmailPolicy',
+    'default',
+    'strict',
+    'SMTP',
+    'HTTP',
+    ]
 
-default = compat32
+class EmailPolicy(Policy):
+
+    """+
+    PROVISIONAL
+
+    The API extensions enabled by this this policy are currently provisional.
+    Refer to the documentation for details.
+
+    This policy adds new header parsing and folding algorithms.  Instead of
+    simple strings, headers are custom objects with custom attributes
+    depending on the type of the field.  The folding algorithm fully
+    implements RFCs 2047 and 5322.
+
+    In addition to the settable attributes listed above that apply to
+    all Policies, this policy adds the following additional attributes:
+
+    refold_source       -- if the value for a header in the Message object
+                           came from the parsing of some source, this attribute
+                           indicates whether or not a generator should refold
+                           that value when transforming the message back into
+                           stream form.  The possible values are:
+
+                           none  -- all source values use original folding
+                           long  -- source values that have any line that is
+                                    longer than max_line_length will be
+                                    refolded
+                           all  -- all values are refolded.
+
+                           The default is 'long'.
+
+    header_factory      -- a callable that takes two arguments, 'name' and
+                           'value', where 'name' is a header field name and
+                           'value' is an unfolded header field value, and
+                           returns a string-like object that represents that
+                           header.  A default header_factory is provided that
+                           understands some of the RFC5322 header field types.
+                           (Currently address fields and date fields have
+                           special treatment, while all other fields are
+                           treated as unstructured.  This list will be
+                           completed before the extension is marked stable.)
+    """
+
+    refold_source = 'long'
+    header_factory = _HeaderRegistry()
+
+    def __init__(self, **kw):
+        # Ensure that each new instance gets a unique header factory
+        # (as opposed to clones, which share the factory).
+        if 'header_factory' not in kw:
+            object.__setattr__(self, 'header_factory', _HeaderRegistry())
+        super().__init__(**kw)
+
+    # The logic of the next three methods is chosen such that it is possible to
+    # switch a Message object between a Compat32 policy and a policy derived
+    # from this class and have the results stay consistent.  This allows a
+    # Message object constructed with this policy to be passed to a library
+    # that only handles Compat32 objects, or to receive such an object and
+    # convert it to use the newer style by just changing its policy.  It is
+    # also chosen because it postpones the relatively expensive full rfc5322
+    # parse until as late as possible when parsing from source, since in many
+    # applications only a few headers will actually be inspected.
+
+    def header_source_parse(self, sourcelines):
+        """+
+        The name is parsed as everything up to the ':' and returned unmodified.
+        The value is determined by stripping leading whitespace off the
+        remainder of the first line, joining all subsequent lines together, and
+        stripping any trailing carriage return or linefeed characters.  (This
+        is the same as Compat32).
+
+        """
+        name, value = sourcelines[0].split(':', 1)
+        value = value.lstrip(' \t') + ''.join(sourcelines[1:])
+        return (name, value.rstrip('\r\n'))
+
+    def header_store_parse(self, name, value):
+        """+
+        The name is returned unchanged.  If the input value has a 'name'
+        attribute and it matches the name ignoring case, the value is returned
+        unchanged.  Otherwise the name and value are passed to header_factory
+        method, and the resulting custom header object is returned as the
+        value.  In this case a ValueError is raised if the input value contains
+        CR or LF characters.
+
+        """
+        if hasattr(value, 'name') and value.name.lower() == name.lower():
+            return (name, value)
+        if len(value.splitlines())>1:
+            raise ValueError("Header values may not contain linefeed "
+                             "or carriage return characters")
+        return (name, self.header_factory(name, value))
+
+    def header_fetch_parse(self, name, value):
+        """+
+        If the value has a 'name' attribute, it is returned to unmodified.
+        Otherwise the name and the value with any linesep characters removed
+        are passed to the header_factory method, and the resulting custom
+        header object is returned.  Any surrogateescaped bytes get turned
+        into the unicode unknown-character glyph.
+
+        """
+        if hasattr(value, 'name'):
+            return value
+        return self.header_factory(name, ''.join(value.splitlines()))
+
+    def fold(self, name, value):
+        """+
+        Header folding is controlled by the refold_source policy setting.  A
+        value is considered to be a 'source value' if and only if it does not
+        have a 'name' attribute (having a 'name' attribute means it is a header
+        object of some sort).  If a source value needs to be refolded according
+        to the policy, it is converted into a custom header object by passing
+        the name and the value with any linesep characters removed to the
+        header_factory method.  Folding of a custom header object is done by
+        calling its fold method with the current policy.
+
+        Source values are split into lines using splitlines.  If the value is
+        not to be refolded, the lines are rejoined using the linesep from the
+        policy and returned.  The exception is lines containing non-ascii
+        binary data.  In that case the value is refolded regardless of the
+        refold_source setting, which causes the binary data to be CTE encoded
+        using the unknown-8bit charset.
+
+        """
+        return self._fold(name, value, refold_binary=True)
+
+    def fold_binary(self, name, value):
+        """+
+        The same as fold if cte_type is 7bit, except that the returned value is
+        bytes.
+
+        If cte_type is 8bit, non-ASCII binary data is converted back into
+        bytes.  Headers with binary data are not refolded, regardless of the
+        refold_header setting, since there is no way to know whether the binary
+        data consists of single byte characters or multibyte characters.
+
+        """
+        folded = self._fold(name, value, refold_binary=self.cte_type=='7bit')
+        return folded.encode('ascii', 'surrogateescape')
+
+    def _fold(self, name, value, refold_binary=False):
+        if hasattr(value, 'name'):
+            return value.fold(policy=self)
+        maxlen = self.max_line_length if self.max_line_length else float('inf')
+        lines = value.splitlines()
+        refold = (self.refold_source == 'all' or
+                  self.refold_source == 'long' and
+                    (len(lines[0])+len(name)+2 > maxlen or
+                     any(len(x) > maxlen for x in lines[1:])))
+        if refold or refold_binary and _has_surrogates(value):
+            return self.header_factory(name, ''.join(lines)).fold(policy=self)
+        return name + ': ' + self.linesep.join(lines) + self.linesep
+
+
+default = EmailPolicy()
+# Make the default policy use the class default header_factory
+del default.header_factory
 strict = default.clone(raise_on_defect=True)
 SMTP = default.clone(linesep='\r\n')
 HTTP = default.clone(linesep='\r\n', max_line_length=None)
diff --git a/Lib/email/utils.py b/Lib/email/utils.py
index b82d5c5..b7e1bb9 100644
--- a/Lib/email/utils.py
+++ b/Lib/email/utils.py
@@ -62,6 +62,13 @@ escapesre = re.compile(r'[\\"]')
 _has_surrogates = re.compile(
     '([^\ud800-\udbff]|\A)[\udc00-\udfff]([^\udc00-\udfff]|\Z)').search
 
+# How to deal with a string containing bytes before handing it to the
+# application through the 'normal' interface.
+def _sanitize(string):
+    # Turn any escaped bytes into unicode 'unknown' char.
+    original_bytes = string.encode('ascii', 'surrogateescape')
+    return original_bytes.decode('ascii', 'replace')
+
 
 # Helpers
 
diff --git a/Lib/test/test_email/__init__.py b/Lib/test/test_email/__init__.py
index b05fb3c..75dc64d 100644
--- a/Lib/test/test_email/__init__.py
+++ b/Lib/test/test_email/__init__.py
@@ -65,3 +65,9 @@ class TestEmailBase(unittest.TestCase):
     def assertBytesEqual(self, first, second, msg):
         """Our byte strings are really encoded strings; improve diff output"""
         self.assertEqual(self._bytes_repr(first), self._bytes_repr(second))
+
+    def assertDefectsEqual(self, actual, expected):
+        self.assertEqual(len(actual), len(expected), actual)
+        for i in range(len(actual)):
+            self.assertIsInstance(actual[i], expected[i],
+                                    'item {}'.format(i))
diff --git a/Lib/test/test_email/test__encoded_words.py b/Lib/test/test_email/test__encoded_words.py
new file mode 100644
index 0000000..14395fe
--- /dev/null
+++ b/Lib/test/test_email/test__encoded_words.py
@@ -0,0 +1,187 @@
+import unittest
+from email import _encoded_words as _ew
+from email import errors
+from test.test_email import TestEmailBase
+
+
+class TestDecodeQ(TestEmailBase):
+
+    def _test(self, source, ex_result, ex_defects=[]):
+        result, defects = _ew.decode_q(source)
+        self.assertEqual(result, ex_result)
+        self.assertDefectsEqual(defects, ex_defects)
+
+    def test_no_encoded(self):
+        self._test(b'foobar', b'foobar')
+
+    def test_spaces(self):
+        self._test(b'foo=20bar=20', b'foo bar ')
+        self._test(b'foo_bar_', b'foo bar ')
+
+    def test_run_of_encoded(self):
+        self._test(b'foo=20=20=21=2Cbar', b'foo  !,bar')
+
+
+class TestDecodeB(TestEmailBase):
+
+    def _test(self, source, ex_result, ex_defects=[]):
+        result, defects = _ew.decode_b(source)
+        self.assertEqual(result, ex_result)
+        self.assertDefectsEqual(defects, ex_defects)
+
+    def test_simple(self):
+        self._test(b'Zm9v', b'foo')
+
+    def test_missing_padding(self):
+        self._test(b'dmk', b'vi', [errors.InvalidBase64PaddingDefect])
+
+    def test_invalid_character(self):
+        self._test(b'dm\x01k===', b'vi', [errors.InvalidBase64CharactersDefect])
+
+    def test_invalid_character_and_bad_padding(self):
+        self._test(b'dm\x01k', b'vi', [errors.InvalidBase64CharactersDefect,
+                                       errors.InvalidBase64PaddingDefect])
+
+
+class TestDecode(TestEmailBase):
+
+    def test_wrong_format_input_raises(self):
+        with self.assertRaises(ValueError):
+            _ew.decode('=?badone?=')
+        with self.assertRaises(ValueError):
+            _ew.decode('=?')
+        with self.assertRaises(ValueError):
+            _ew.decode('')
+
+    def _test(self, source, result, charset='us-ascii', lang='', defects=[]):
+        res, char, l, d = _ew.decode(source)
+        self.assertEqual(res, result)
+        self.assertEqual(char, charset)
+        self.assertEqual(l, lang)
+        self.assertDefectsEqual(d, defects)
+
+    def test_simple_q(self):
+        self._test('=?us-ascii?q?foo?=', 'foo')
+
+    def test_simple_b(self):
+        self._test('=?us-ascii?b?dmk=?=', 'vi')
+
+    def test_q_case_ignored(self):
+        self._test('=?us-ascii?Q?foo?=', 'foo')
+
+    def test_b_case_ignored(self):
+        self._test('=?us-ascii?B?dmk=?=', 'vi')
+
+    def test_non_trivial_q(self):
+        self._test('=?latin-1?q?=20F=fcr=20Elise=20?=', ' Für Elise ', 'latin-1')
+
+    def test_q_escpaed_bytes_preserved(self):
+        self._test(b'=?us-ascii?q?=20\xACfoo?='.decode('us-ascii',
+                                                       'surrogateescape'),
+                   ' \uDCACfoo',
+                   defects = [errors.UndecodableBytesDefect])
+
+    def test_b_undecodable_bytes_ignored_with_defect(self):
+        self._test(b'=?us-ascii?b?dm\xACk?='.decode('us-ascii',
+                                                   'surrogateescape'),
+                   'vi',
+                   defects = [
+                    errors.InvalidBase64CharactersDefect,
+                    errors.InvalidBase64PaddingDefect])
+
+    def test_b_invalid_bytes_ignored_with_defect(self):
+        self._test('=?us-ascii?b?dm\x01k===?=',
+                   'vi',
+                   defects = [errors.InvalidBase64CharactersDefect])
+
+    def test_b_invalid_bytes_incorrect_padding(self):
+        self._test('=?us-ascii?b?dm\x01k?=',
+                   'vi',
+                   defects = [
+                    errors.InvalidBase64CharactersDefect,
+                    errors.InvalidBase64PaddingDefect])
+
+    def test_b_padding_defect(self):
+        self._test('=?us-ascii?b?dmk?=',
+                   'vi',
+                    defects = [errors.InvalidBase64PaddingDefect])
+
+    def test_nonnull_lang(self):
+        self._test('=?us-ascii*jive?q?test?=', 'test', lang='jive')
+
+    def test_unknown_8bit_charset(self):
+        self._test('=?unknown-8bit?q?foo=ACbar?=',
+                   b'foo\xacbar'.decode('ascii', 'surrogateescape'),
+                   charset = 'unknown-8bit',
+                   defects = [])
+
+    def test_unknown_charset(self):
+        self._test('=?foobar?q?foo=ACbar?=',
+                   b'foo\xacbar'.decode('ascii', 'surrogateescape'),
+                   charset = 'foobar',
+                   # XXX Should this be a new Defect instead?
+                   defects = [errors.CharsetError])
+
+
+class TestEncodeQ(TestEmailBase):
+
+    def _test(self, src, expected):
+        self.assertEqual(_ew.encode_q(src), expected)
+
+    def test_all_safe(self):
+        self._test(b'foobar', 'foobar')
+
+    def test_spaces(self):
+        self._test(b'foo bar ', 'foo_bar_')
+
+    def test_run_of_encodables(self):
+        self._test(b'foo  ,,bar', 'foo__=2C=2Cbar')
+
+
+class TestEncodeB(TestEmailBase):
+
+    def test_simple(self):
+        self.assertEqual(_ew.encode_b(b'foo'), 'Zm9v')
+
+    def test_padding(self):
+        self.assertEqual(_ew.encode_b(b'vi'), 'dmk=')
+
+
+class TestEncode(TestEmailBase):
+
+    def test_q(self):
+        self.assertEqual(_ew.encode('foo', 'utf-8', 'q'), '=?utf-8?q?foo?=')
+
+    def test_b(self):
+        self.assertEqual(_ew.encode('foo', 'utf-8', 'b'), '=?utf-8?b?Zm9v?=')
+
+    def test_auto_q(self):
+        self.assertEqual(_ew.encode('foo', 'utf-8'), '=?utf-8?q?foo?=')
+
+    def test_auto_q_if_short_mostly_safe(self):
+        self.assertEqual(_ew.encode('vi.', 'utf-8'), '=?utf-8?q?vi=2E?=')
+
+    def test_auto_b_if_enough_unsafe(self):
+        self.assertEqual(_ew.encode('.....', 'utf-8'), '=?utf-8?b?Li4uLi4=?=')
+
+    def test_auto_b_if_long_unsafe(self):
+        self.assertEqual(_ew.encode('vi.vi.vi.vi.vi.', 'utf-8'),
+                         '=?utf-8?b?dmkudmkudmkudmkudmku?=')
+
+    def test_auto_q_if_long_mostly_safe(self):
+        self.assertEqual(_ew.encode('vi vi vi.vi ', 'utf-8'),
+                         '=?utf-8?q?vi_vi_vi=2Evi_?=')
+
+    def test_utf8_default(self):
+        self.assertEqual(_ew.encode('foo'), '=?utf-8?q?foo?=')
+
+    def test_lang(self):
+        self.assertEqual(_ew.encode('foo', lang='jive'), '=?utf-8*jive?q?foo?=')
+
+    def test_unknown_8bit(self):
+        self.assertEqual(_ew.encode('foo\uDCACbar', charset='unknown-8bit'),
+                         '=?unknown-8bit?q?foo=ACbar?=')
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/Lib/test/test_email/test__header_value_parser.py b/Lib/test/test_email/test__header_value_parser.py
new file mode 100644
index 0000000..75fe299
--- /dev/null
+++ b/Lib/test/test_email/test__header_value_parser.py
@@ -0,0 +1,2466 @@
+import string
+import unittest
+from email import _header_value_parser as parser
+from email import errors
+from email import policy
+from test.test_email import TestEmailBase
+
+class TestTokens(TestEmailBase):
+
+    # EWWhiteSpaceTerminal
+
+    def test_EWWhiteSpaceTerminal(self):
+        x = parser.EWWhiteSpaceTerminal(' \t', 'fws')
+        self.assertEqual(x, ' \t')
+        self.assertEqual(str(x), '')
+        self.assertEqual(x.value, '')
+        self.assertEqual(x.encoded, ' \t')
+
+    # UnstructuredTokenList
+
+    def test_undecodable_bytes_error_preserved(self):
+        badstr = b"le pouf c\xaflebre".decode('ascii', 'surrogateescape')
+        unst = parser.get_unstructured(badstr)
+        self.assertDefectsEqual(unst.all_defects, [errors.UndecodableBytesDefect])
+        parts = list(unst.parts)
+        self.assertDefectsEqual(parts[0].all_defects, [])
+        self.assertDefectsEqual(parts[1].all_defects, [])
+        self.assertDefectsEqual(parts[2].all_defects, [errors.UndecodableBytesDefect])
+
+
+class TestParser(TestEmailBase):
+
+    # _wsp_splitter
+
+    rfc_printable_ascii = bytes(range(33, 127)).decode('ascii')
+    rfc_atext_chars = (string.ascii_letters + string.digits +
+                        "!#$%&\'*+-/=?^_`{}|~")
+    rfc_dtext_chars = rfc_printable_ascii.translate(str.maketrans('','',r'\[]'))
+
+    def test__wsp_splitter_one_word(self):
+        self.assertEqual(parser._wsp_splitter('foo', 1), ['foo'])
+
+    def test__wsp_splitter_two_words(self):
+        self.assertEqual(parser._wsp_splitter('foo def', 1),
+                                               ['foo', ' ', 'def'])
+
+    def test__wsp_splitter_ws_runs(self):
+        self.assertEqual(parser._wsp_splitter('foo \t def jik', 1),
+                                              ['foo', ' \t ', 'def jik'])
+
+
+    # test harness
+
+    def _test_get_x(self, method, input, string, value, defects,
+                          remainder, comments=None):
+        token, rest = method(input)
+        self.assertEqual(str(token), string)
+        self.assertEqual(token.value, value)
+        self.assertDefectsEqual(token.all_defects, defects)
+        self.assertEqual(rest, remainder)
+        if comments is not None:
+            self.assertEqual(token.comments, comments)
+        return token
+
+    # get_fws
+
+    def test_get_fws_only(self):
+        fws = self._test_get_x(parser.get_fws, ' \t  ', ' \t  ', ' ', [], '')
+        self.assertEqual(fws.token_type, 'fws')
+
+    def test_get_fws_space(self):
+        self._test_get_x(parser.get_fws, ' foo', ' ', ' ', [], 'foo')
+
+    def test_get_fws_ws_run(self):
+        self._test_get_x(parser.get_fws, ' \t foo ', ' \t ', ' ', [], 'foo ')
+
+    # get_encoded_word
+
+    def test_get_encoded_word_missing_start_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_encoded_word('abc')
+
+    def test_get_encoded_word_missing_end_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_encoded_word('=?abc')
+
+    def test_get_encoded_word_missing_middle_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_encoded_word('=?abc?=')
+
+    def test_get_encoded_word_valid_ew(self):
+        self._test_get_x(parser.get_encoded_word,
+                         '=?us-ascii?q?this_is_a_test?=  bird',
+                         'this is a test',
+                         'this is a test',
+                         [],
+                         '  bird')
+
+    def test_get_encoded_word_internal_spaces(self):
+        self._test_get_x(parser.get_encoded_word,
+                         '=?us-ascii?q?this is a test?=  bird',
+                         'this is a test',
+                         'this is a test',
+                         [errors.InvalidHeaderDefect],
+                         '  bird')
+
+    def test_get_encoded_word_gets_first(self):
+        self._test_get_x(parser.get_encoded_word,
+                         '=?us-ascii?q?first?=  =?utf-8?q?second?=',
+                         'first',
+                         'first',
+                         [],
+                         '  =?utf-8?q?second?=')
+
+    def test_get_encoded_word_gets_first_even_if_no_space(self):
+        self._test_get_x(parser.get_encoded_word,
+                         '=?us-ascii?q?first?==?utf-8?q?second?=',
+                         'first',
+                         'first',
+                         [],
+                         '=?utf-8?q?second?=')
+
+    def test_get_encoded_word_sets_extra_attributes(self):
+        ew = self._test_get_x(parser.get_encoded_word,
+                         '=?us-ascii*jive?q?first_second?=',
+                         'first second',
+                         'first second',
+                         [],
+                         '')
+        self.assertEqual(ew.encoded, '=?us-ascii*jive?q?first_second?=')
+        self.assertEqual(ew.charset, 'us-ascii')
+        self.assertEqual(ew.lang, 'jive')
+
+    def test_get_encoded_word_lang_default_is_blank(self):
+        ew = self._test_get_x(parser.get_encoded_word,
+                         '=?us-ascii?q?first_second?=',
+                         'first second',
+                         'first second',
+                         [],
+                         '')
+        self.assertEqual(ew.encoded, '=?us-ascii?q?first_second?=')
+        self.assertEqual(ew.charset, 'us-ascii')
+        self.assertEqual(ew.lang, '')
+
+    def test_get_encoded_word_non_printable_defect(self):
+        self._test_get_x(parser.get_encoded_word,
+                         '=?us-ascii?q?first\x02second?=',
+                         'first\x02second',
+                         'first\x02second',
+                         [errors.NonPrintableDefect],
+                         '')
+
+    def test_get_encoded_word_leading_internal_space(self):
+        self._test_get_x(parser.get_encoded_word,
+                        '=?us-ascii?q?=20foo?=',
+                        ' foo',
+                        ' foo',
+                        [],
+                        '')
+
+    # get_unstructured
+
+    def _get_unst(self, value):
+        token = parser.get_unstructured(value)
+        return token, ''
+
+    def test_get_unstructured_null(self):
+        self._test_get_x(self._get_unst, '', '', '', [], '')
+
+    def test_get_unstructured_one_word(self):
+        self._test_get_x(self._get_unst, 'foo', 'foo', 'foo', [], '')
+
+    def test_get_unstructured_normal_phrase(self):
+        self._test_get_x(self._get_unst, 'foo bar bird',
+                                         'foo bar bird',
+                                         'foo bar bird',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_normal_phrase_with_whitespace(self):
+        self._test_get_x(self._get_unst, 'foo \t bar      bird',
+                                         'foo \t bar      bird',
+                                         'foo bar bird',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_leading_whitespace(self):
+        self._test_get_x(self._get_unst, '  foo bar',
+                                         '  foo bar',
+                                         ' foo bar',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_trailing_whitespace(self):
+        self._test_get_x(self._get_unst, 'foo bar  ',
+                                         'foo bar  ',
+                                         'foo bar ',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_leading_and_trailing_whitespace(self):
+        self._test_get_x(self._get_unst, '  foo bar  ',
+                                         '  foo bar  ',
+                                         ' foo bar ',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_one_valid_ew_no_ws(self):
+        self._test_get_x(self._get_unst, '=?us-ascii?q?bar?=',
+                                         'bar',
+                                         'bar',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_one_ew_trailing_ws(self):
+        self._test_get_x(self._get_unst, '=?us-ascii?q?bar?=  ',
+                                         'bar  ',
+                                         'bar ',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_one_valid_ew_trailing_text(self):
+        self._test_get_x(self._get_unst, '=?us-ascii?q?bar?= bird',
+                                         'bar bird',
+                                         'bar bird',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_phrase_with_ew_in_middle_of_text(self):
+        self._test_get_x(self._get_unst, 'foo =?us-ascii?q?bar?= bird',
+                                         'foo bar bird',
+                                         'foo bar bird',
+                                         [],
+                                         '')
+
+    def test_get_unstructured_phrase_with_two_ew(self):
+        self._test_get_x(self._get_unst,
+            'foo =?us-ascii?q?bar?= =?us-ascii?q?bird?=',
+            'foo barbird',
+            'foo barbird',
+            [],
+            '')
+
+    def test_get_unstructured_phrase_with_two_ew_trailing_ws(self):
+        self._test_get_x(self._get_unst,
+            'foo =?us-ascii?q?bar?= =?us-ascii?q?bird?=   ',
+            'foo barbird   ',
+            'foo barbird ',
+            [],
+            '')
+
+    def test_get_unstructured_phrase_with_ew_with_leading_ws(self):
+        self._test_get_x(self._get_unst,
+            '  =?us-ascii?q?bar?=',
+            '  bar',
+            ' bar',
+            [],
+            '')
+
+    def test_get_unstructured_phrase_with_two_ew_extra_ws(self):
+        self._test_get_x(self._get_unst,
+            'foo =?us-ascii?q?bar?= \t  =?us-ascii?q?bird?=',
+            'foo barbird',
+            'foo barbird',
+            [],
+            '')
+
+    def test_get_unstructured_two_ew_extra_ws_trailing_text(self):
+        self._test_get_x(self._get_unst,
+            '=?us-ascii?q?test?=   =?us-ascii?q?foo?=  val',
+            'testfoo  val',
+            'testfoo val',
+            [],
+            '')
+
+    def test_get_unstructured_ew_with_internal_ws(self):
+        self._test_get_x(self._get_unst,
+            '=?iso-8859-1?q?hello=20world?=',
+            'hello world',
+            'hello world',
+            [],
+            '')
+
+    def test_get_unstructured_ew_with_internal_leading_ws(self):
+        self._test_get_x(self._get_unst,
+            '   =?us-ascii?q?=20test?=   =?us-ascii?q?=20foo?=  val',
+            '    test foo  val',
+            '  test foo val',
+            [],
+            '')
+
+    def test_get_unstructured_invaild_ew(self):
+        self._test_get_x(self._get_unst,
+            '=?test val',
+            '=?test val',
+            '=?test val',
+            [],
+            '')
+
+    def test_get_unstructured_undecodable_bytes(self):
+        self._test_get_x(self._get_unst,
+            b'test \xACfoo  val'.decode('ascii', 'surrogateescape'),
+            'test \uDCACfoo  val',
+            'test \uDCACfoo val',
+            [errors.UndecodableBytesDefect],
+            '')
+
+    def test_get_unstructured_undecodable_bytes_in_EW(self):
+        self._test_get_x(self._get_unst,
+            (b'=?us-ascii?q?=20test?=   =?us-ascii?q?=20\xACfoo?='
+                b'  val').decode('ascii', 'surrogateescape'),
+            ' test \uDCACfoo  val',
+            ' test \uDCACfoo val',
+            [errors.UndecodableBytesDefect]*2,
+            '')
+
+    def test_get_unstructured_missing_base64_padding(self):
+        self._test_get_x(self._get_unst,
+            '=?utf-8?b?dmk?=',
+            'vi',
+            'vi',
+            [errors.InvalidBase64PaddingDefect],
+            '')
+
+    def test_get_unstructured_invalid_base64_character(self):
+        self._test_get_x(self._get_unst,
+            '=?utf-8?b?dm\x01k===?=',
+            'vi',
+            'vi',
+            [errors.InvalidBase64CharactersDefect],
+            '')
+
+    def test_get_unstructured_invalid_base64_character_and_bad_padding(self):
+        self._test_get_x(self._get_unst,
+            '=?utf-8?b?dm\x01k?=',
+            'vi',
+            'vi',
+            [errors.InvalidBase64CharactersDefect,
+             errors.InvalidBase64PaddingDefect],
+            '')
+
+    def test_get_unstructured_no_whitespace_between_ews(self):
+        self._test_get_x(self._get_unst,
+            '=?utf-8?q?foo?==?utf-8?q?bar?=',
+            'foobar',
+            'foobar',
+            [errors.InvalidHeaderDefect],
+            '')
+
+    # get_qp_ctext
+
+    def test_get_qp_ctext_only(self):
+        ptext = self._test_get_x(parser.get_qp_ctext,
+                                'foobar', 'foobar', ' ', [], '')
+        self.assertEqual(ptext.token_type, 'ptext')
+
+    def test_get_qp_ctext_all_printables(self):
+        with_qp = self.rfc_printable_ascii.replace('\\', '\\\\')
+        with_qp = with_qp.  replace('(', r'\(')
+        with_qp = with_qp.replace(')', r'\)')
+        ptext = self._test_get_x(parser.get_qp_ctext,
+                                 with_qp, self.rfc_printable_ascii, ' ', [], '')
+
+    def test_get_qp_ctext_two_words_gets_first(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo de', 'foo', ' ', [], ' de')
+
+    def test_get_qp_ctext_following_wsp_preserved(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo \t\tde', 'foo', ' ', [], ' \t\tde')
+
+    def test_get_qp_ctext_up_to_close_paren_only(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo)', 'foo', ' ', [], ')')
+
+    def test_get_qp_ctext_wsp_before_close_paren_preserved(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo  )', 'foo', ' ', [], '  )')
+
+    def test_get_qp_ctext_close_paren_mid_word(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo)bar', 'foo', ' ', [], ')bar')
+
+    def test_get_qp_ctext_up_to_open_paren_only(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo(', 'foo', ' ', [], '(')
+
+    def test_get_qp_ctext_wsp_before_open_paren_preserved(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo  (', 'foo', ' ', [], '  (')
+
+    def test_get_qp_ctext_open_paren_mid_word(self):
+        self._test_get_x(parser.get_qp_ctext,
+                        'foo(bar', 'foo', ' ', [], '(bar')
+
+    def test_get_qp_ctext_non_printables(self):
+        ptext = self._test_get_x(parser.get_qp_ctext,
+                                'foo\x00bar)', 'foo\x00bar', ' ',
+                                [errors.NonPrintableDefect], ')')
+        self.assertEqual(ptext.defects[0].non_printables[0], '\x00')
+
+    # get_qcontent
+
+    def test_get_qcontent_only(self):
+        ptext = self._test_get_x(parser.get_qcontent,
+                                'foobar', 'foobar', 'foobar', [], '')
+        self.assertEqual(ptext.token_type, 'ptext')
+
+    def test_get_qcontent_all_printables(self):
+        with_qp = self.rfc_printable_ascii.replace('\\', '\\\\')
+        with_qp = with_qp.  replace('"', r'\"')
+        ptext = self._test_get_x(parser.get_qcontent, with_qp,
+                                 self.rfc_printable_ascii,
+                                 self.rfc_printable_ascii, [], '')
+
+    def test_get_qcontent_two_words_gets_first(self):
+        self._test_get_x(parser.get_qcontent,
+                        'foo de', 'foo', 'foo', [], ' de')
+
+    def test_get_qcontent_following_wsp_preserved(self):
+        self._test_get_x(parser.get_qcontent,
+                        'foo \t\tde', 'foo', 'foo', [], ' \t\tde')
+
+    def test_get_qcontent_up_to_dquote_only(self):
+        self._test_get_x(parser.get_qcontent,
+                        'foo"', 'foo', 'foo', [], '"')
+
+    def test_get_qcontent_wsp_before_close_paren_preserved(self):
+        self._test_get_x(parser.get_qcontent,
+                        'foo  "', 'foo', 'foo', [], '  "')
+
+    def test_get_qcontent_close_paren_mid_word(self):
+        self._test_get_x(parser.get_qcontent,
+                        'foo"bar', 'foo', 'foo', [], '"bar')
+
+    def test_get_qcontent_non_printables(self):
+        ptext = self._test_get_x(parser.get_qcontent,
+                                'foo\x00fg"', 'foo\x00fg', 'foo\x00fg',
+                                [errors.NonPrintableDefect], '"')
+        self.assertEqual(ptext.defects[0].non_printables[0], '\x00')
+
+    # get_atext
+
+    def test_get_atext_only(self):
+        atext = self._test_get_x(parser.get_atext,
+                                'foobar', 'foobar', 'foobar', [], '')
+        self.assertEqual(atext.token_type, 'atext')
+
+    def test_get_atext_all_atext(self):
+        atext = self._test_get_x(parser.get_atext, self.rfc_atext_chars,
+                                 self.rfc_atext_chars,
+                                 self.rfc_atext_chars, [], '')
+
+    def test_get_atext_two_words_gets_first(self):
+        self._test_get_x(parser.get_atext,
+                        'foo bar', 'foo', 'foo', [], ' bar')
+
+    def test_get_atext_following_wsp_preserved(self):
+        self._test_get_x(parser.get_atext,
+                        'foo \t\tbar', 'foo', 'foo', [], ' \t\tbar')
+
+    def test_get_atext_up_to_special(self):
+        self._test_get_x(parser.get_atext,
+                        'foo@bar', 'foo', 'foo', [], '@bar')
+
+    def test_get_atext_non_printables(self):
+        atext = self._test_get_x(parser.get_atext,
+                                'foo\x00bar(', 'foo\x00bar', 'foo\x00bar',
+                                [errors.NonPrintableDefect], '(')
+        self.assertEqual(atext.defects[0].non_printables[0], '\x00')
+
+    # get_bare_quoted_string
+
+    def test_get_bare_quoted_string_only(self):
+        bqs = self._test_get_x(parser.get_bare_quoted_string,
+                               '"foo"', '"foo"', 'foo', [], '')
+        self.assertEqual(bqs.token_type, 'bare-quoted-string')
+
+    def test_get_bare_quoted_string_must_start_with_dquote(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_bare_quoted_string('foo"')
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_bare_quoted_string('  "foo"')
+
+    def test_get_bare_quoted_string_following_wsp_preserved(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+             '"foo"\t bar', '"foo"', 'foo', [], '\t bar')
+
+    def test_get_bare_quoted_string_multiple_words(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+             '"foo bar moo"', '"foo bar moo"', 'foo bar moo', [], '')
+
+    def test_get_bare_quoted_string_multiple_words_wsp_preserved(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+             '" foo  moo\t"', '" foo  moo\t"', ' foo  moo\t', [], '')
+
+    def test_get_bare_quoted_string_end_dquote_mid_word(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+             '"foo"bar', '"foo"', 'foo', [], 'bar')
+
+    def test_get_bare_quoted_string_quoted_dquote(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+             r'"foo\"in"a', r'"foo\"in"', 'foo"in', [], 'a')
+
+    def test_get_bare_quoted_string_non_printables(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+             '"a\x01a"', '"a\x01a"', 'a\x01a',
+             [errors.NonPrintableDefect], '')
+
+    def test_get_bare_quoted_string_no_end_dquote(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+             '"foo', '"foo"', 'foo',
+             [errors.InvalidHeaderDefect], '')
+        self._test_get_x(parser.get_bare_quoted_string,
+             '"foo ', '"foo "', 'foo ',
+             [errors.InvalidHeaderDefect], '')
+
+    def test_get_bare_quoted_string_empty_quotes(self):
+        self._test_get_x(parser.get_bare_quoted_string,
+            '""', '""', '', [], '')
+
+    # get_comment
+
+    def test_get_comment_only(self):
+        comment = self._test_get_x(parser.get_comment,
+            '(comment)', '(comment)', ' ', [], '', ['comment'])
+        self.assertEqual(comment.token_type, 'comment')
+
+    def test_get_comment_must_start_with_paren(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_comment('foo"')
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_comment('  (foo"')
+
+    def test_get_comment_following_wsp_preserved(self):
+        self._test_get_x(parser.get_comment,
+            '(comment)  \t', '(comment)', ' ', [], '  \t', ['comment'])
+
+    def test_get_comment_multiple_words(self):
+        self._test_get_x(parser.get_comment,
+            '(foo bar)  \t', '(foo bar)', ' ', [], '  \t', ['foo bar'])
+
+    def test_get_comment_multiple_words_wsp_preserved(self):
+        self._test_get_x(parser.get_comment,
+            '( foo  bar\t )  \t', '( foo  bar\t )', ' ', [], '  \t',
+                [' foo  bar\t '])
+
+    def test_get_comment_end_paren_mid_word(self):
+        self._test_get_x(parser.get_comment,
+            '(foo)bar', '(foo)', ' ', [], 'bar', ['foo'])
+
+    def test_get_comment_quoted_parens(self):
+        self._test_get_x(parser.get_comment,
+            '(foo\) \(\)bar)', '(foo\) \(\)bar)', ' ', [], '', ['foo) ()bar'])
+
+    def test_get_comment_non_printable(self):
+        self._test_get_x(parser.get_comment,
+            '(foo\x7Fbar)', '(foo\x7Fbar)', ' ',
+            [errors.NonPrintableDefect], '', ['foo\x7Fbar'])
+
+    def test_get_comment_no_end_paren(self):
+        self._test_get_x(parser.get_comment,
+            '(foo bar', '(foo bar)', ' ',
+            [errors.InvalidHeaderDefect], '', ['foo bar'])
+        self._test_get_x(parser.get_comment,
+            '(foo bar  ', '(foo bar  )', ' ',
+            [errors.InvalidHeaderDefect], '', ['foo bar  '])
+
+    def test_get_comment_nested_comment(self):
+        comment = self._test_get_x(parser.get_comment,
+            '(foo(bar))', '(foo(bar))', ' ', [], '', ['foo(bar)'])
+        self.assertEqual(comment[1].content, 'bar')
+
+    def test_get_comment_nested_comment_wsp(self):
+        comment = self._test_get_x(parser.get_comment,
+            '(foo ( bar ) )', '(foo ( bar ) )', ' ', [], '', ['foo ( bar ) '])
+        self.assertEqual(comment[2].content, ' bar ')
+
+    def test_get_comment_empty_comment(self):
+        self._test_get_x(parser.get_comment,
+            '()', '()', ' ', [], '', [''])
+
+    def test_get_comment_multiple_nesting(self):
+        comment = self._test_get_x(parser.get_comment,
+            '(((((foo)))))', '(((((foo)))))', ' ', [], '', ['((((foo))))'])
+        for i in range(4, 0, -1):
+            self.assertEqual(comment[0].content, '('*(i-1)+'foo'+')'*(i-1))
+            comment = comment[0]
+        self.assertEqual(comment.content, 'foo')
+
+    def test_get_comment_missing_end_of_nesting(self):
+        self._test_get_x(parser.get_comment,
+            '(((((foo)))', '(((((foo)))))', ' ',
+            [errors.InvalidHeaderDefect]*2, '', ['((((foo))))'])
+
+    def test_get_comment_qs_in_nested_comment(self):
+        comment = self._test_get_x(parser.get_comment,
+            '(foo (b\)))', '(foo (b\)))', ' ', [], '', ['foo (b\))'])
+        self.assertEqual(comment[2].content, 'b)')
+
+    # get_cfws
+
+    def test_get_cfws_only_ws(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            '  \t \t', '  \t \t', ' ', [], '', [])
+        self.assertEqual(cfws.token_type, 'cfws')
+
+    def test_get_cfws_only_comment(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            '(foo)', '(foo)', ' ', [], '', ['foo'])
+        self.assertEqual(cfws[0].content, 'foo')
+
+    def test_get_cfws_only_mixed(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            ' (foo )  ( bar) ', ' (foo )  ( bar) ', ' ', [], '',
+                ['foo ', ' bar'])
+        self.assertEqual(cfws[1].content, 'foo ')
+        self.assertEqual(cfws[3].content, ' bar')
+
+    def test_get_cfws_ends_at_non_leader(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            '(foo) bar', '(foo) ', ' ', [], 'bar', ['foo'])
+        self.assertEqual(cfws[0].content, 'foo')
+
+    def test_get_cfws_ends_at_non_printable(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            '(foo) \x07', '(foo) ', ' ', [], '\x07', ['foo'])
+        self.assertEqual(cfws[0].content, 'foo')
+
+    def test_get_cfws_non_printable_in_comment(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            '(foo \x07) "test"', '(foo \x07) ', ' ',
+            [errors.NonPrintableDefect], '"test"', ['foo \x07'])
+        self.assertEqual(cfws[0].content, 'foo \x07')
+
+    def test_get_cfws_header_ends_in_comment(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            '  (foo ', '  (foo )', ' ',
+            [errors.InvalidHeaderDefect], '', ['foo '])
+        self.assertEqual(cfws[1].content, 'foo ')
+
+    def test_get_cfws_multiple_nested_comments(self):
+        cfws = self._test_get_x(parser.get_cfws,
+            '(foo (bar)) ((a)(a))', '(foo (bar)) ((a)(a))', ' ', [],
+                '', ['foo (bar)', '(a)(a)'])
+        self.assertEqual(cfws[0].comments, ['foo (bar)'])
+        self.assertEqual(cfws[2].comments, ['(a)(a)'])
+
+    # get_quoted_string
+
+    def test_get_quoted_string_only(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            '"bob"', '"bob"', 'bob', [], '')
+        self.assertEqual(qs.token_type, 'quoted-string')
+        self.assertEqual(qs.quoted_value, '"bob"')
+        self.assertEqual(qs.content, 'bob')
+
+    def test_get_quoted_string_with_wsp(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            '\t "bob"  ', '\t "bob"  ', ' bob ', [], '')
+        self.assertEqual(qs.quoted_value, ' "bob" ')
+        self.assertEqual(qs.content, 'bob')
+
+    def test_get_quoted_string_with_comments_and_wsp(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            ' (foo) "bob"(bar)', ' (foo) "bob"(bar)', ' bob ', [], '')
+        self.assertEqual(qs[0][1].content, 'foo')
+        self.assertEqual(qs[2][0].content, 'bar')
+        self.assertEqual(qs.content, 'bob')
+        self.assertEqual(qs.quoted_value, ' "bob" ')
+
+    def test_get_quoted_string_with_multiple_comments(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            ' (foo) (bar) "bob"(bird)', ' (foo) (bar) "bob"(bird)', ' bob ',
+                [], '')
+        self.assertEqual(qs[0].comments, ['foo', 'bar'])
+        self.assertEqual(qs[2].comments, ['bird'])
+        self.assertEqual(qs.content, 'bob')
+        self.assertEqual(qs.quoted_value, ' "bob" ')
+
+    def test_get_quoted_string_non_printable_in_comment(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            ' (\x0A) "bob"', ' (\x0A) "bob"', ' bob',
+                [errors.NonPrintableDefect], '')
+        self.assertEqual(qs[0].comments, ['\x0A'])
+        self.assertEqual(qs.content, 'bob')
+        self.assertEqual(qs.quoted_value, ' "bob"')
+
+    def test_get_quoted_string_non_printable_in_qcontent(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            ' (a) "a\x0B"', ' (a) "a\x0B"', ' a\x0B',
+                [errors.NonPrintableDefect], '')
+        self.assertEqual(qs[0].comments, ['a'])
+        self.assertEqual(qs.content, 'a\x0B')
+        self.assertEqual(qs.quoted_value, ' "a\x0B"')
+
+    def test_get_quoted_string_internal_ws(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            ' (a) "foo  bar "', ' (a) "foo  bar "', ' foo  bar ',
+                [], '')
+        self.assertEqual(qs[0].comments, ['a'])
+        self.assertEqual(qs.content, 'foo  bar ')
+        self.assertEqual(qs.quoted_value, ' "foo  bar "')
+
+    def test_get_quoted_string_header_ends_in_comment(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            ' (a) "bob" (a', ' (a) "bob" (a)', ' bob ',
+                [errors.InvalidHeaderDefect], '')
+        self.assertEqual(qs[0].comments, ['a'])
+        self.assertEqual(qs[2].comments, ['a'])
+        self.assertEqual(qs.content, 'bob')
+        self.assertEqual(qs.quoted_value, ' "bob" ')
+
+    def test_get_quoted_string_header_ends_in_qcontent(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            ' (a) "bob', ' (a) "bob"', ' bob',
+                [errors.InvalidHeaderDefect], '')
+        self.assertEqual(qs[0].comments, ['a'])
+        self.assertEqual(qs.content, 'bob')
+        self.assertEqual(qs.quoted_value, ' "bob"')
+
+    def test_get_quoted_string_no_quoted_string(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_quoted_string(' (ab) xyz')
+
+    def test_get_quoted_string_qs_ends_at_noncfws(self):
+        qs = self._test_get_x(parser.get_quoted_string,
+            '\t "bob" fee', '\t "bob" ', ' bob ', [], 'fee')
+        self.assertEqual(qs.content, 'bob')
+        self.assertEqual(qs.quoted_value, ' "bob" ')
+
+    # get_atom
+
+    def test_get_atom_only(self):
+        atom = self._test_get_x(parser.get_atom,
+            'bob', 'bob', 'bob', [], '')
+        self.assertEqual(atom.token_type, 'atom')
+
+    def test_get_atom_with_wsp(self):
+        self._test_get_x(parser.get_atom,
+            '\t bob  ', '\t bob  ', ' bob ', [], '')
+
+    def test_get_atom_with_comments_and_wsp(self):
+        atom = self._test_get_x(parser.get_atom,
+            ' (foo) bob(bar)', ' (foo) bob(bar)', ' bob ', [], '')
+        self.assertEqual(atom[0][1].content, 'foo')
+        self.assertEqual(atom[2][0].content, 'bar')
+
+    def test_get_atom_with_multiple_comments(self):
+        atom = self._test_get_x(parser.get_atom,
+            ' (foo) (bar) bob(bird)', ' (foo) (bar) bob(bird)', ' bob ',
+                [], '')
+        self.assertEqual(atom[0].comments, ['foo', 'bar'])
+        self.assertEqual(atom[2].comments, ['bird'])
+
+    def test_get_atom_non_printable_in_comment(self):
+        atom = self._test_get_x(parser.get_atom,
+            ' (\x0A) bob', ' (\x0A) bob', ' bob',
+                [errors.NonPrintableDefect], '')
+        self.assertEqual(atom[0].comments, ['\x0A'])
+
+    def test_get_atom_non_printable_in_atext(self):
+        atom = self._test_get_x(parser.get_atom,
+            ' (a) a\x0B', ' (a) a\x0B', ' a\x0B',
+                [errors.NonPrintableDefect], '')
+        self.assertEqual(atom[0].comments, ['a'])
+
+    def test_get_atom_header_ends_in_comment(self):
+        atom = self._test_get_x(parser.get_atom,
+            ' (a) bob (a', ' (a) bob (a)', ' bob ',
+                [errors.InvalidHeaderDefect], '')
+        self.assertEqual(atom[0].comments, ['a'])
+        self.assertEqual(atom[2].comments, ['a'])
+
+    def test_get_atom_no_atom(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_atom(' (ab) ')
+
+    def test_get_atom_no_atom_before_special(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_atom(' (ab) @')
+
+    def test_get_atom_atom_ends_at_special(self):
+        atom = self._test_get_x(parser.get_atom,
+            ' (foo) bob(bar)  @bang', ' (foo) bob(bar)  ', ' bob ', [], '@bang')
+        self.assertEqual(atom[0].comments, ['foo'])
+        self.assertEqual(atom[2].comments, ['bar'])
+
+    def test_get_atom_atom_ends_at_noncfws(self):
+        atom = self._test_get_x(parser.get_atom,
+            'bob  fred', 'bob  ', 'bob ', [], 'fred')
+
+    # get_dot_atom_text
+
+    def test_get_dot_atom_text(self):
+        dot_atom_text = self._test_get_x(parser.get_dot_atom_text,
+            'foo.bar.bang', 'foo.bar.bang', 'foo.bar.bang', [], '')
+        self.assertEqual(dot_atom_text.token_type, 'dot-atom-text')
+        self.assertEqual(len(dot_atom_text), 5)
+
+    def test_get_dot_atom_text_lone_atom_is_valid(self):
+        dot_atom_text = self._test_get_x(parser.get_dot_atom_text,
+            'foo', 'foo', 'foo', [], '')
+
+    def test_get_dot_atom_text_raises_on_leading_dot(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom_text('.foo.bar')
+
+    def test_get_dot_atom_text_raises_on_trailing_dot(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom_text('foo.bar.')
+
+    def test_get_dot_atom_text_raises_on_leading_non_atext(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom_text(' foo.bar')
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom_text('@foo.bar')
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom_text('"foo.bar"')
+
+    def test_get_dot_atom_text_trailing_text_preserved(self):
+        dot_atom_text = self._test_get_x(parser.get_dot_atom_text,
+            'foo@bar', 'foo', 'foo', [], '@bar')
+
+    def test_get_dot_atom_text_trailing_ws_preserved(self):
+        dot_atom_text = self._test_get_x(parser.get_dot_atom_text,
+            'foo .bar', 'foo', 'foo', [], ' .bar')
+
+    # get_dot_atom
+
+    def test_get_dot_atom_only(self):
+        dot_atom = self._test_get_x(parser.get_dot_atom,
+            'foo.bar.bing', 'foo.bar.bing', 'foo.bar.bing', [], '')
+        self.assertEqual(dot_atom.token_type, 'dot-atom')
+        self.assertEqual(len(dot_atom), 1)
+
+    def test_get_dot_atom_with_wsp(self):
+        self._test_get_x(parser.get_dot_atom,
+            '\t  foo.bar.bing  ', '\t  foo.bar.bing  ', ' foo.bar.bing ', [], '')
+
+    def test_get_dot_atom_with_comments_and_wsp(self):
+        self._test_get_x(parser.get_dot_atom,
+            ' (sing)  foo.bar.bing (here) ', ' (sing)  foo.bar.bing (here) ',
+                ' foo.bar.bing ', [], '')
+
+    def test_get_dot_atom_space_ends_dot_atom(self):
+        self._test_get_x(parser.get_dot_atom,
+            ' (sing)  foo.bar .bing (here) ', ' (sing)  foo.bar ',
+                ' foo.bar ', [], '.bing (here) ')
+
+    def test_get_dot_atom_no_atom_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom(' (foo) ')
+
+    def test_get_dot_atom_leading_dot_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom(' (foo) .bar')
+
+    def test_get_dot_atom_two_dots_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom('bar..bang')
+
+    def test_get_dot_atom_trailing_dot_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_dot_atom(' (foo) bar.bang. foo')
+
+    # get_word (if this were black box we'd repeat all the qs/atom tests)
+
+    def test_get_word_atom_yields_atom(self):
+        word = self._test_get_x(parser.get_word,
+            ' (foo) bar (bang) :ah', ' (foo) bar (bang) ', ' bar ', [], ':ah')
+        self.assertEqual(word.token_type, 'atom')
+        self.assertEqual(word[0].token_type, 'cfws')
+
+    def test_get_word_qs_yields_qs(self):
+        word = self._test_get_x(parser.get_word,
+            '"bar " (bang) ah', '"bar " (bang) ', 'bar  ', [], 'ah')
+        self.assertEqual(word.token_type, 'quoted-string')
+        self.assertEqual(word[0].token_type, 'bare-quoted-string')
+        self.assertEqual(word[0].value, 'bar ')
+        self.assertEqual(word.content, 'bar ')
+
+    def test_get_word_ends_at_dot(self):
+        self._test_get_x(parser.get_word,
+            'foo.', 'foo', 'foo', [], '.')
+
+    # get_phrase
+
+    def test_get_phrase_simple(self):
+        phrase = self._test_get_x(parser.get_phrase,
+            '"Fred A. Johnson" is his name, oh.',
+            '"Fred A. Johnson" is his name',
+            'Fred A. Johnson is his name',
+            [],
+            ', oh.')
+        self.assertEqual(phrase.token_type, 'phrase')
+
+    def test_get_phrase_complex(self):
+        phrase = self._test_get_x(parser.get_phrase,
+            ' (A) bird (in (my|your)) "hand  " is messy\t<>\t',
+            ' (A) bird (in (my|your)) "hand  " is messy\t',
+            ' bird hand   is messy ',
+            [],
+            '<>\t')
+        self.assertEqual(phrase[0][0].comments, ['A'])
+        self.assertEqual(phrase[0][2].comments, ['in (my|your)'])
+
+    def test_get_phrase_obsolete(self):
+        phrase = self._test_get_x(parser.get_phrase,
+            'Fred A.(weird).O Johnson',
+            'Fred A.(weird).O Johnson',
+            'Fred A. .O Johnson',
+            [errors.ObsoleteHeaderDefect]*3,
+            '')
+        self.assertEqual(len(phrase), 7)
+        self.assertEqual(phrase[3].comments, ['weird'])
+
+    def test_get_phrase_pharse_must_start_with_word(self):
+        phrase = self._test_get_x(parser.get_phrase,
+            '(even weirder).name',
+            '(even weirder).name',
+            ' .name',
+            [errors.InvalidHeaderDefect] + [errors.ObsoleteHeaderDefect]*2,
+            '')
+        self.assertEqual(len(phrase), 3)
+        self.assertEqual(phrase[0].comments, ['even weirder'])
+
+    def test_get_phrase_ending_with_obsolete(self):
+        phrase = self._test_get_x(parser.get_phrase,
+            'simple phrase.(with trailing comment):boo',
+            'simple phrase.(with trailing comment)',
+            'simple phrase. ',
+            [errors.ObsoleteHeaderDefect]*2,
+            ':boo')
+        self.assertEqual(len(phrase), 4)
+        self.assertEqual(phrase[3].comments, ['with trailing comment'])
+
+    def get_phrase_cfws_only_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_phrase(' (foo) ')
+
+    # get_local_part
+
+    def test_get_local_part_simple(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            'dinsdale@python.org', 'dinsdale', 'dinsdale', [], '@python.org')
+        self.assertEqual(local_part.token_type, 'local-part')
+        self.assertEqual(local_part.local_part, 'dinsdale')
+
+    def test_get_local_part_with_dot(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            'Fred.A.Johnson@python.org',
+            'Fred.A.Johnson',
+            'Fred.A.Johnson',
+            [],
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred.A.Johnson')
+
+    def test_get_local_part_with_whitespace(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' Fred.A.Johnson  @python.org',
+            ' Fred.A.Johnson  ',
+            ' Fred.A.Johnson ',
+            [],
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred.A.Johnson')
+
+    def test_get_local_part_with_cfws(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' (foo) Fred.A.Johnson (bar (bird))  @python.org',
+            ' (foo) Fred.A.Johnson (bar (bird))  ',
+            ' Fred.A.Johnson ',
+            [],
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred.A.Johnson')
+        self.assertEqual(local_part[0][0].comments, ['foo'])
+        self.assertEqual(local_part[0][2].comments, ['bar (bird)'])
+
+    def test_get_local_part_simple_quoted(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            '"dinsdale"@python.org', '"dinsdale"', '"dinsdale"', [], '@python.org')
+        self.assertEqual(local_part.token_type, 'local-part')
+        self.assertEqual(local_part.local_part, 'dinsdale')
+
+    def test_get_local_part_with_quoted_dot(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            '"Fred.A.Johnson"@python.org',
+            '"Fred.A.Johnson"',
+            '"Fred.A.Johnson"',
+            [],
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred.A.Johnson')
+
+    def test_get_local_part_quoted_with_whitespace(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' "Fred A. Johnson"  @python.org',
+            ' "Fred A. Johnson"  ',
+            ' "Fred A. Johnson" ',
+            [],
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred A. Johnson')
+
+    def test_get_local_part_quoted_with_cfws(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' (foo) " Fred A. Johnson " (bar (bird))  @python.org',
+            ' (foo) " Fred A. Johnson " (bar (bird))  ',
+            ' " Fred A. Johnson " ',
+            [],
+            '@python.org')
+        self.assertEqual(local_part.local_part, ' Fred A. Johnson ')
+        self.assertEqual(local_part[0][0].comments, ['foo'])
+        self.assertEqual(local_part[0][2].comments, ['bar (bird)'])
+
+
+    def test_get_local_part_simple_obsolete(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            'Fred. A.Johnson@python.org',
+            'Fred. A.Johnson',
+            'Fred. A.Johnson',
+            [errors.ObsoleteHeaderDefect],
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred.A.Johnson')
+
+    def test_get_local_part_complex_obsolete_1(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' (foo )Fred (bar).(bird) A.(sheep)Johnson."and  dogs "@python.org',
+            ' (foo )Fred (bar).(bird) A.(sheep)Johnson."and  dogs "',
+            ' Fred . A. Johnson.and  dogs ',
+            [errors.ObsoleteHeaderDefect],
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred.A.Johnson.and  dogs ')
+
+    def test_get_local_part_complex_obsolete_invalid(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' (foo )Fred (bar).(bird) A.(sheep)Johnson "and  dogs"@python.org',
+            ' (foo )Fred (bar).(bird) A.(sheep)Johnson "and  dogs"',
+            ' Fred . A. Johnson and  dogs',
+            [errors.InvalidHeaderDefect]*2,
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'Fred.A.Johnson and  dogs')
+
+    def test_get_local_part_no_part_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_local_part(' (foo) ')
+
+    def test_get_local_part_special_instead_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_local_part(' (foo) @python.org')
+
+    def test_get_local_part_trailing_dot(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' borris.@python.org',
+            ' borris.',
+            ' borris.',
+            [errors.InvalidHeaderDefect]*2,
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'borris.')
+
+    def test_get_local_part_trailing_dot_with_ws(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' borris. @python.org',
+            ' borris. ',
+            ' borris. ',
+            [errors.InvalidHeaderDefect]*2,
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'borris.')
+
+    def test_get_local_part_leading_dot(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            '.borris@python.org',
+            '.borris',
+            '.borris',
+            [errors.InvalidHeaderDefect]*2,
+            '@python.org')
+        self.assertEqual(local_part.local_part, '.borris')
+
+    def test_get_local_part_leading_dot_after_ws(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' .borris@python.org',
+            ' .borris',
+            ' .borris',
+            [errors.InvalidHeaderDefect]*2,
+            '@python.org')
+        self.assertEqual(local_part.local_part, '.borris')
+
+    def test_get_local_part_double_dot_raises(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            ' borris.(foo).natasha@python.org',
+            ' borris.(foo).natasha',
+            ' borris. .natasha',
+            [errors.InvalidHeaderDefect]*2,
+            '@python.org')
+        self.assertEqual(local_part.local_part, 'borris..natasha')
+
+    def test_get_local_part_quoted_strings_in_atom_list(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            '""example" example"@example.com',
+            '""example" example"',
+            'example example',
+            [errors.InvalidHeaderDefect]*3,
+            '@example.com')
+        self.assertEqual(local_part.local_part, 'example example')
+
+    def test_get_local_part_valid_and_invalid_qp_in_atom_list(self):
+        local_part = self._test_get_x(parser.get_local_part,
+            r'"\\"example\\" example"@example.com',
+            r'"\\"example\\" example"',
+            r'\example\\ example',
+            [errors.InvalidHeaderDefect]*5,
+            '@example.com')
+        self.assertEqual(local_part.local_part, r'\example\\ example')
+
+    def test_get_local_part_unicode_defect(self):
+        # Currently this only happens when parsing unicode, not when parsing
+        # stuff that was originally binary.
+        local_part = self._test_get_x(parser.get_local_part,
+            'exámple@example.com',
+            'exámple',
+            'exámple',
+            [errors.NonASCIILocalPartDefect],
+            '@example.com')
+        self.assertEqual(local_part.local_part, 'exámple')
+
+    # get_dtext
+
+    def test_get_dtext_only(self):
+        dtext = self._test_get_x(parser.get_dtext,
+                                'foobar', 'foobar', 'foobar', [], '')
+        self.assertEqual(dtext.token_type, 'ptext')
+
+    def test_get_dtext_all_dtext(self):
+        dtext = self._test_get_x(parser.get_dtext, self.rfc_dtext_chars,
+                                 self.rfc_dtext_chars,
+                                 self.rfc_dtext_chars, [], '')
+
+    def test_get_dtext_two_words_gets_first(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo bar', 'foo', 'foo', [], ' bar')
+
+    def test_get_dtext_following_wsp_preserved(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo \t\tbar', 'foo', 'foo', [], ' \t\tbar')
+
+    def test_get_dtext_non_printables(self):
+        dtext = self._test_get_x(parser.get_dtext,
+                                'foo\x00bar]', 'foo\x00bar', 'foo\x00bar',
+                                [errors.NonPrintableDefect], ']')
+        self.assertEqual(dtext.defects[0].non_printables[0], '\x00')
+
+    def test_get_dtext_with_qp(self):
+        ptext = self._test_get_x(parser.get_dtext,
+                                 r'foo\]\[\\bar\b\e\l\l',
+                                 r'foo][\barbell',
+                                 r'foo][\barbell',
+                                 [errors.ObsoleteHeaderDefect],
+                                 '')
+
+    def test_get_dtext_up_to_close_bracket_only(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo]', 'foo', 'foo', [], ']')
+
+    def test_get_dtext_wsp_before_close_bracket_preserved(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo  ]', 'foo', 'foo', [], '  ]')
+
+    def test_get_dtext_close_bracket_mid_word(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo]bar', 'foo', 'foo', [], ']bar')
+
+    def test_get_dtext_up_to_open_bracket_only(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo[', 'foo', 'foo', [], '[')
+
+    def test_get_dtext_wsp_before_open_bracket_preserved(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo  [', 'foo', 'foo', [], '  [')
+
+    def test_get_dtext_open_bracket_mid_word(self):
+        self._test_get_x(parser.get_dtext,
+                        'foo[bar', 'foo', 'foo', [], '[bar')
+
+    # get_domain_literal
+
+    def test_get_domain_literal_only(self):
+        domain_literal = domain_literal = self._test_get_x(parser.get_domain_literal,
+                                '[127.0.0.1]',
+                                '[127.0.0.1]',
+                                '[127.0.0.1]',
+                                [],
+                                '')
+        self.assertEqual(domain_literal.token_type, 'domain-literal')
+        self.assertEqual(domain_literal.domain, '[127.0.0.1]')
+        self.assertEqual(domain_literal.ip, '127.0.0.1')
+
+    def test_get_domain_literal_with_internal_ws(self):
+        domain_literal = self._test_get_x(parser.get_domain_literal,
+                                '[  127.0.0.1\t ]',
+                                '[  127.0.0.1\t ]',
+                                '[ 127.0.0.1 ]',
+                                [],
+                                '')
+        self.assertEqual(domain_literal.domain, '[127.0.0.1]')
+        self.assertEqual(domain_literal.ip, '127.0.0.1')
+
+    def test_get_domain_literal_with_surrounding_cfws(self):
+        domain_literal = self._test_get_x(parser.get_domain_literal,
+                                '(foo)[  127.0.0.1] (bar)',
+                                '(foo)[  127.0.0.1] (bar)',
+                                ' [ 127.0.0.1] ',
+                                [],
+                                '')
+        self.assertEqual(domain_literal.domain, '[127.0.0.1]')
+        self.assertEqual(domain_literal.ip, '127.0.0.1')
+
+    def test_get_domain_literal_no_start_char_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_domain_literal('(foo) ')
+
+    def test_get_domain_literal_no_start_char_before_special_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_domain_literal('(foo) @')
+
+    def test_get_domain_literal_bad_dtext_char_before_special_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_domain_literal('(foo) [abc[@')
+
+    # get_domain
+
+    def test_get_domain_regular_domain_only(self):
+        domain = self._test_get_x(parser.get_domain,
+                                  'example.com',
+                                  'example.com',
+                                  'example.com',
+                                  [],
+                                  '')
+        self.assertEqual(domain.token_type, 'domain')
+        self.assertEqual(domain.domain, 'example.com')
+
+    def test_get_domain_domain_literal_only(self):
+        domain = self._test_get_x(parser.get_domain,
+                                  '[127.0.0.1]',
+                                  '[127.0.0.1]',
+                                  '[127.0.0.1]',
+                                  [],
+                                  '')
+        self.assertEqual(domain.token_type, 'domain')
+        self.assertEqual(domain.domain, '[127.0.0.1]')
+
+    def test_get_domain_with_cfws(self):
+        domain = self._test_get_x(parser.get_domain,
+                                  '(foo) example.com(bar)\t',
+                                  '(foo) example.com(bar)\t',
+                                  ' example.com ',
+                                  [],
+                                  '')
+        self.assertEqual(domain.domain, 'example.com')
+
+    def test_get_domain_domain_literal_with_cfws(self):
+        domain = self._test_get_x(parser.get_domain,
+                                  '(foo)[127.0.0.1]\t(bar)',
+                                  '(foo)[127.0.0.1]\t(bar)',
+                                  ' [127.0.0.1] ',
+                                  [],
+                                  '')
+        self.assertEqual(domain.domain, '[127.0.0.1]')
+
+    def test_get_domain_domain_with_cfws_ends_at_special(self):
+        domain = self._test_get_x(parser.get_domain,
+                                  '(foo)example.com\t(bar), next',
+                                  '(foo)example.com\t(bar)',
+                                  ' example.com ',
+                                  [],
+                                  ', next')
+        self.assertEqual(domain.domain, 'example.com')
+
+    def test_get_domain_domain_literal_with_cfws_ends_at_special(self):
+        domain = self._test_get_x(parser.get_domain,
+                                  '(foo)[127.0.0.1]\t(bar), next',
+                                  '(foo)[127.0.0.1]\t(bar)',
+                                  ' [127.0.0.1] ',
+                                  [],
+                                  ', next')
+        self.assertEqual(domain.domain, '[127.0.0.1]')
+
+    def test_get_domain_obsolete(self):
+        domain = self._test_get_x(parser.get_domain,
+                                  '(foo) example . (bird)com(bar)\t',
+                                  '(foo) example . (bird)com(bar)\t',
+                                  ' example . com ',
+                                  [errors.ObsoleteHeaderDefect],
+                                  '')
+        self.assertEqual(domain.domain, 'example.com')
+
+    def test_get_domain_no_non_cfws_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_domain("  (foo)\t")
+
+    def test_get_domain_no_atom_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_domain("  (foo)\t, broken")
+
+
+    # get_addr_spec
+
+    def test_get_addr_spec_normal(self):
+        addr_spec = self._test_get_x(parser.get_addr_spec,
+                                    'dinsdale@example.com',
+                                    'dinsdale@example.com',
+                                    'dinsdale@example.com',
+                                    [],
+                                    '')
+        self.assertEqual(addr_spec.token_type, 'addr-spec')
+        self.assertEqual(addr_spec.local_part, 'dinsdale')
+        self.assertEqual(addr_spec.domain, 'example.com')
+        self.assertEqual(addr_spec.addr_spec, 'dinsdale@example.com')
+
+    def test_get_addr_spec_with_doamin_literal(self):
+        addr_spec = self._test_get_x(parser.get_addr_spec,
+                                    'dinsdale@[127.0.0.1]',
+                                    'dinsdale@[127.0.0.1]',
+                                    'dinsdale@[127.0.0.1]',
+                                    [],
+                                    '')
+        self.assertEqual(addr_spec.local_part, 'dinsdale')
+        self.assertEqual(addr_spec.domain, '[127.0.0.1]')
+        self.assertEqual(addr_spec.addr_spec, 'dinsdale@[127.0.0.1]')
+
+    def test_get_addr_spec_with_cfws(self):
+        addr_spec = self._test_get_x(parser.get_addr_spec,
+                '(foo) dinsdale(bar)@ (bird) example.com (bog)',
+                '(foo) dinsdale(bar)@ (bird) example.com (bog)',
+                ' dinsdale@example.com ',
+                [],
+                '')
+        self.assertEqual(addr_spec.local_part, 'dinsdale')
+        self.assertEqual(addr_spec.domain, 'example.com')
+        self.assertEqual(addr_spec.addr_spec, 'dinsdale@example.com')
+
+    def test_get_addr_spec_with_qouoted_string_and_cfws(self):
+        addr_spec = self._test_get_x(parser.get_addr_spec,
+                '(foo) "roy a bug"(bar)@ (bird) example.com (bog)',
+                '(foo) "roy a bug"(bar)@ (bird) example.com (bog)',
+                ' "roy a bug"@example.com ',
+                [],
+                '')
+        self.assertEqual(addr_spec.local_part, 'roy a bug')
+        self.assertEqual(addr_spec.domain, 'example.com')
+        self.assertEqual(addr_spec.addr_spec, '"roy a bug"@example.com')
+
+    def test_get_addr_spec_ends_at_special(self):
+        addr_spec = self._test_get_x(parser.get_addr_spec,
+                '(foo) "roy a bug"(bar)@ (bird) example.com (bog) , next',
+                '(foo) "roy a bug"(bar)@ (bird) example.com (bog) ',
+                ' "roy a bug"@example.com ',
+                [],
+                ', next')
+        self.assertEqual(addr_spec.local_part, 'roy a bug')
+        self.assertEqual(addr_spec.domain, 'example.com')
+        self.assertEqual(addr_spec.addr_spec, '"roy a bug"@example.com')
+
+    def test_get_addr_spec_quoted_strings_in_atom_list(self):
+        addr_spec = self._test_get_x(parser.get_addr_spec,
+            '""example" example"@example.com',
+            '""example" example"@example.com',
+            'example example@example.com',
+            [errors.InvalidHeaderDefect]*3,
+            '')
+        self.assertEqual(addr_spec.local_part, 'example example')
+        self.assertEqual(addr_spec.domain, 'example.com')
+        self.assertEqual(addr_spec.addr_spec, '"example example"@example.com')
+
+    def test_get_addr_spec_dot_atom(self):
+        addr_spec = self._test_get_x(parser.get_addr_spec,
+            'star.a.star@example.com',
+            'star.a.star@example.com',
+            'star.a.star@example.com',
+            [],
+            '')
+        self.assertEqual(addr_spec.local_part, 'star.a.star')
+        self.assertEqual(addr_spec.domain, 'example.com')
+        self.assertEqual(addr_spec.addr_spec, 'star.a.star@example.com')
+
+    # get_obs_route
+
+    def test_get_obs_route_simple(self):
+        obs_route = self._test_get_x(parser.get_obs_route,
+            '@example.com, @two.example.com:',
+            '@example.com, @two.example.com:',
+            '@example.com, @two.example.com:',
+            [],
+            '')
+        self.assertEqual(obs_route.token_type, 'obs-route')
+        self.assertEqual(obs_route.domains, ['example.com', 'two.example.com'])
+
+    def test_get_obs_route_complex(self):
+        obs_route = self._test_get_x(parser.get_obs_route,
+            '(foo),, (blue)@example.com (bar),@two.(foo) example.com (bird):',
+            '(foo),, (blue)@example.com (bar),@two.(foo) example.com (bird):',
+            ' ,, @example.com ,@two. example.com :',
+            [errors.ObsoleteHeaderDefect],  # This is the obs-domain
+            '')
+        self.assertEqual(obs_route.token_type, 'obs-route')
+        self.assertEqual(obs_route.domains, ['example.com', 'two.example.com'])
+
+    def test_get_obs_route_no_route_before_end_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_obs_route('(foo) @example.com,')
+
+    def test_get_obs_route_no_route_before_special_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_obs_route('(foo) [abc],')
+
+    def test_get_obs_route_no_route_before_special_raises2(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_obs_route('(foo) @example.com [abc],')
+
+    # get_angle_addr
+
+    def test_get_angle_addr_simple(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '<dinsdale@example.com>',
+            '<dinsdale@example.com>',
+            '<dinsdale@example.com>',
+            [],
+            '')
+        self.assertEqual(angle_addr.token_type, 'angle-addr')
+        self.assertEqual(angle_addr.local_part, 'dinsdale')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_angle_addr_with_cfws(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            ' (foo) <dinsdale@example.com>(bar)',
+            ' (foo) <dinsdale@example.com>(bar)',
+            ' <dinsdale@example.com> ',
+            [],
+            '')
+        self.assertEqual(angle_addr.token_type, 'angle-addr')
+        self.assertEqual(angle_addr.local_part, 'dinsdale')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_angle_addr_qs_and_domain_literal(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '<"Fred Perfect"@[127.0.0.1]>',
+            '<"Fred Perfect"@[127.0.0.1]>',
+            '<"Fred Perfect"@[127.0.0.1]>',
+            [],
+            '')
+        self.assertEqual(angle_addr.local_part, 'Fred Perfect')
+        self.assertEqual(angle_addr.domain, '[127.0.0.1]')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, '"Fred Perfect"@[127.0.0.1]')
+
+    def test_get_angle_addr_internal_cfws(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '<(foo) dinsdale@example.com(bar)>',
+            '<(foo) dinsdale@example.com(bar)>',
+            '< dinsdale@example.com >',
+            [],
+            '')
+        self.assertEqual(angle_addr.local_part, 'dinsdale')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_angle_addr_obs_route(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '(foo)<@example.com, (bird) @two.example.com: dinsdale@example.com> (bar) ',
+            '(foo)<@example.com, (bird) @two.example.com: dinsdale@example.com> (bar) ',
+            ' <@example.com, @two.example.com: dinsdale@example.com> ',
+            [errors.ObsoleteHeaderDefect],
+            '')
+        self.assertEqual(angle_addr.local_part, 'dinsdale')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertEqual(angle_addr.route, ['example.com', 'two.example.com'])
+        self.assertEqual(angle_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_angle_addr_missing_closing_angle(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '<dinsdale@example.com',
+            '<dinsdale@example.com>',
+            '<dinsdale@example.com>',
+            [errors.InvalidHeaderDefect],
+            '')
+        self.assertEqual(angle_addr.local_part, 'dinsdale')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_angle_addr_missing_closing_angle_with_cfws(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '<dinsdale@example.com (foo)',
+            '<dinsdale@example.com (foo)>',
+            '<dinsdale@example.com >',
+            [errors.InvalidHeaderDefect],
+            '')
+        self.assertEqual(angle_addr.local_part, 'dinsdale')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_angle_addr_ends_at_special(self):
+        angle_addr = self._test_get_x(parser.get_angle_addr,
+            '<dinsdale@example.com> (foo), next',
+            '<dinsdale@example.com> (foo)',
+            '<dinsdale@example.com> ',
+            [],
+            ', next')
+        self.assertEqual(angle_addr.local_part, 'dinsdale')
+        self.assertEqual(angle_addr.domain, 'example.com')
+        self.assertIsNone(angle_addr.route)
+        self.assertEqual(angle_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_angle_addr_no_angle_raise(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_angle_addr('(foo) ')
+
+    def test_get_angle_addr_no_angle_before_special_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_angle_addr('(foo) , next')
+
+    def test_get_angle_addr_no_angle_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_angle_addr('bar')
+
+    def test_get_angle_addr_special_after_angle_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_angle_addr('(foo) <, bar')
+
+    # get_display_name  This is phrase but with a different value.
+
+    def test_get_display_name_simple(self):
+        display_name = self._test_get_x(parser.get_display_name,
+            'Fred A Johnson',
+            'Fred A Johnson',
+            'Fred A Johnson',
+            [],
+            '')
+        self.assertEqual(display_name.token_type, 'display-name')
+        self.assertEqual(display_name.display_name, 'Fred A Johnson')
+
+    def test_get_display_name_complex1(self):
+        display_name = self._test_get_x(parser.get_display_name,
+            '"Fred A. Johnson" is his name, oh.',
+            '"Fred A. Johnson" is his name',
+            '"Fred A. Johnson is his name"',
+            [],
+            ', oh.')
+        self.assertEqual(display_name.token_type, 'display-name')
+        self.assertEqual(display_name.display_name, 'Fred A. Johnson is his name')
+
+    def test_get_display_name_complex2(self):
+        display_name = self._test_get_x(parser.get_display_name,
+            ' (A) bird (in (my|your)) "hand  " is messy\t<>\t',
+            ' (A) bird (in (my|your)) "hand  " is messy\t',
+            ' "bird hand   is messy" ',
+            [],
+            '<>\t')
+        self.assertEqual(display_name[0][0].comments, ['A'])
+        self.assertEqual(display_name[0][2].comments, ['in (my|your)'])
+        self.assertEqual(display_name.display_name, 'bird hand   is messy')
+
+    def test_get_display_name_obsolete(self):
+        display_name = self._test_get_x(parser.get_display_name,
+            'Fred A.(weird).O Johnson',
+            'Fred A.(weird).O Johnson',
+            '"Fred A. .O Johnson"',
+            [errors.ObsoleteHeaderDefect]*3,
+            '')
+        self.assertEqual(len(display_name), 7)
+        self.assertEqual(display_name[3].comments, ['weird'])
+        self.assertEqual(display_name.display_name, 'Fred A. .O Johnson')
+
+    def test_get_display_name_pharse_must_start_with_word(self):
+        display_name = self._test_get_x(parser.get_display_name,
+            '(even weirder).name',
+            '(even weirder).name',
+            ' ".name"',
+            [errors.InvalidHeaderDefect] + [errors.ObsoleteHeaderDefect]*2,
+            '')
+        self.assertEqual(len(display_name), 3)
+        self.assertEqual(display_name[0].comments, ['even weirder'])
+        self.assertEqual(display_name.display_name, '.name')
+
+    def test_get_display_name_ending_with_obsolete(self):
+        display_name = self._test_get_x(parser.get_display_name,
+            'simple phrase.(with trailing comment):boo',
+            'simple phrase.(with trailing comment)',
+            '"simple phrase." ',
+            [errors.ObsoleteHeaderDefect]*2,
+            ':boo')
+        self.assertEqual(len(display_name), 4)
+        self.assertEqual(display_name[3].comments, ['with trailing comment'])
+        self.assertEqual(display_name.display_name, 'simple phrase.')
+
+    # get_name_addr
+
+    def test_get_name_addr_angle_addr_only(self):
+        name_addr = self._test_get_x(parser.get_name_addr,
+            '<dinsdale@example.com>',
+            '<dinsdale@example.com>',
+            '<dinsdale@example.com>',
+            [],
+            '')
+        self.assertEqual(name_addr.token_type, 'name-addr')
+        self.assertIsNone(name_addr.display_name)
+        self.assertEqual(name_addr.local_part, 'dinsdale')
+        self.assertEqual(name_addr.domain, 'example.com')
+        self.assertIsNone(name_addr.route)
+        self.assertEqual(name_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_name_addr_atom_name(self):
+        name_addr = self._test_get_x(parser.get_name_addr,
+            'Dinsdale <dinsdale@example.com>',
+            'Dinsdale <dinsdale@example.com>',
+            'Dinsdale <dinsdale@example.com>',
+            [],
+            '')
+        self.assertEqual(name_addr.token_type, 'name-addr')
+        self.assertEqual(name_addr.display_name, 'Dinsdale')
+        self.assertEqual(name_addr.local_part, 'dinsdale')
+        self.assertEqual(name_addr.domain, 'example.com')
+        self.assertIsNone(name_addr.route)
+        self.assertEqual(name_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_name_addr_atom_name_with_cfws(self):
+        name_addr = self._test_get_x(parser.get_name_addr,
+            '(foo) Dinsdale (bar) <dinsdale@example.com> (bird)',
+            '(foo) Dinsdale (bar) <dinsdale@example.com> (bird)',
+            ' Dinsdale <dinsdale@example.com> ',
+            [],
+            '')
+        self.assertEqual(name_addr.display_name, 'Dinsdale')
+        self.assertEqual(name_addr.local_part, 'dinsdale')
+        self.assertEqual(name_addr.domain, 'example.com')
+        self.assertIsNone(name_addr.route)
+        self.assertEqual(name_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_name_addr_name_with_cfws_and_dots(self):
+        name_addr = self._test_get_x(parser.get_name_addr,
+            '(foo) Roy.A.Bear (bar) <dinsdale@example.com> (bird)',
+            '(foo) Roy.A.Bear (bar) <dinsdale@example.com> (bird)',
+            ' "Roy.A.Bear" <dinsdale@example.com> ',
+            [errors.ObsoleteHeaderDefect]*2,
+            '')
+        self.assertEqual(name_addr.display_name, 'Roy.A.Bear')
+        self.assertEqual(name_addr.local_part, 'dinsdale')
+        self.assertEqual(name_addr.domain, 'example.com')
+        self.assertIsNone(name_addr.route)
+        self.assertEqual(name_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_name_addr_qs_name(self):
+        name_addr = self._test_get_x(parser.get_name_addr,
+            '"Roy.A.Bear" <dinsdale@example.com>',
+            '"Roy.A.Bear" <dinsdale@example.com>',
+            '"Roy.A.Bear" <dinsdale@example.com>',
+            [],
+            '')
+        self.assertEqual(name_addr.display_name, 'Roy.A.Bear')
+        self.assertEqual(name_addr.local_part, 'dinsdale')
+        self.assertEqual(name_addr.domain, 'example.com')
+        self.assertIsNone(name_addr.route)
+        self.assertEqual(name_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_name_addr_with_route(self):
+        name_addr = self._test_get_x(parser.get_name_addr,
+            '"Roy.A.Bear" <@two.example.com: dinsdale@example.com>',
+            '"Roy.A.Bear" <@two.example.com: dinsdale@example.com>',
+            '"Roy.A.Bear" <@two.example.com: dinsdale@example.com>',
+            [errors.ObsoleteHeaderDefect],
+            '')
+        self.assertEqual(name_addr.display_name, 'Roy.A.Bear')
+        self.assertEqual(name_addr.local_part, 'dinsdale')
+        self.assertEqual(name_addr.domain, 'example.com')
+        self.assertEqual(name_addr.route, ['two.example.com'])
+        self.assertEqual(name_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_name_addr_ends_at_special(self):
+        name_addr = self._test_get_x(parser.get_name_addr,
+            '"Roy.A.Bear" <dinsdale@example.com>, next',
+            '"Roy.A.Bear" <dinsdale@example.com>',
+            '"Roy.A.Bear" <dinsdale@example.com>',
+            [],
+            ', next')
+        self.assertEqual(name_addr.display_name, 'Roy.A.Bear')
+        self.assertEqual(name_addr.local_part, 'dinsdale')
+        self.assertEqual(name_addr.domain, 'example.com')
+        self.assertIsNone(name_addr.route)
+        self.assertEqual(name_addr.addr_spec, 'dinsdale@example.com')
+
+    def test_get_name_addr_no_content_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_name_addr(' (foo) ')
+
+    def test_get_name_addr_no_content_before_special_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_name_addr(' (foo) ,')
+
+    def test_get_name_addr_no_angle_after_display_name_raises(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_name_addr('foo bar')
+
+    # get_mailbox
+
+    def test_get_mailbox_addr_spec_only(self):
+        mailbox = self._test_get_x(parser.get_mailbox,
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            [],
+            '')
+        self.assertEqual(mailbox.token_type, 'mailbox')
+        self.assertIsNone(mailbox.display_name)
+        self.assertEqual(mailbox.local_part, 'dinsdale')
+        self.assertEqual(mailbox.domain, 'example.com')
+        self.assertIsNone(mailbox.route)
+        self.assertEqual(mailbox.addr_spec, 'dinsdale@example.com')
+
+    def test_get_mailbox_angle_addr_only(self):
+        mailbox = self._test_get_x(parser.get_mailbox,
+            '<dinsdale@example.com>',
+            '<dinsdale@example.com>',
+            '<dinsdale@example.com>',
+            [],
+            '')
+        self.assertEqual(mailbox.token_type, 'mailbox')
+        self.assertIsNone(mailbox.display_name)
+        self.assertEqual(mailbox.local_part, 'dinsdale')
+        self.assertEqual(mailbox.domain, 'example.com')
+        self.assertIsNone(mailbox.route)
+        self.assertEqual(mailbox.addr_spec, 'dinsdale@example.com')
+
+    def test_get_mailbox_name_addr(self):
+        mailbox = self._test_get_x(parser.get_mailbox,
+            '"Roy A. Bear" <dinsdale@example.com>',
+            '"Roy A. Bear" <dinsdale@example.com>',
+            '"Roy A. Bear" <dinsdale@example.com>',
+            [],
+            '')
+        self.assertEqual(mailbox.token_type, 'mailbox')
+        self.assertEqual(mailbox.display_name, 'Roy A. Bear')
+        self.assertEqual(mailbox.local_part, 'dinsdale')
+        self.assertEqual(mailbox.domain, 'example.com')
+        self.assertIsNone(mailbox.route)
+        self.assertEqual(mailbox.addr_spec, 'dinsdale@example.com')
+
+    def test_get_mailbox_ends_at_special(self):
+        mailbox = self._test_get_x(parser.get_mailbox,
+            '"Roy A. Bear" <dinsdale@example.com>, rest',
+            '"Roy A. Bear" <dinsdale@example.com>',
+            '"Roy A. Bear" <dinsdale@example.com>',
+            [],
+            ', rest')
+        self.assertEqual(mailbox.token_type, 'mailbox')
+        self.assertEqual(mailbox.display_name, 'Roy A. Bear')
+        self.assertEqual(mailbox.local_part, 'dinsdale')
+        self.assertEqual(mailbox.domain, 'example.com')
+        self.assertIsNone(mailbox.route)
+        self.assertEqual(mailbox.addr_spec, 'dinsdale@example.com')
+
+    def test_get_mailbox_quoted_strings_in_atom_list(self):
+        mailbox = self._test_get_x(parser.get_mailbox,
+            '""example" example"@example.com',
+            '""example" example"@example.com',
+            'example example@example.com',
+            [errors.InvalidHeaderDefect]*3,
+            '')
+        self.assertEqual(mailbox.local_part, 'example example')
+        self.assertEqual(mailbox.domain, 'example.com')
+        self.assertEqual(mailbox.addr_spec, '"example example"@example.com')
+
+    # get_mailbox_list
+
+    def test_get_mailbox_list_single_addr(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            [],
+            '')
+        self.assertEqual(mailbox_list.token_type, 'mailbox-list')
+        self.assertEqual(len(mailbox_list.mailboxes), 1)
+        mailbox = mailbox_list.mailboxes[0]
+        self.assertIsNone(mailbox.display_name)
+        self.assertEqual(mailbox.local_part, 'dinsdale')
+        self.assertEqual(mailbox.domain, 'example.com')
+        self.assertIsNone(mailbox.route)
+        self.assertEqual(mailbox.addr_spec, 'dinsdale@example.com')
+        self.assertEqual(mailbox_list.mailboxes,
+                         mailbox_list.all_mailboxes)
+
+    def test_get_mailbox_list_two_simple_addr(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            'dinsdale@example.com, dinsdale@test.example.com',
+            'dinsdale@example.com, dinsdale@test.example.com',
+            'dinsdale@example.com, dinsdale@test.example.com',
+            [],
+            '')
+        self.assertEqual(mailbox_list.token_type, 'mailbox-list')
+        self.assertEqual(len(mailbox_list.mailboxes), 2)
+        self.assertEqual(mailbox_list.mailboxes[0].addr_spec,
+                        'dinsdale@example.com')
+        self.assertEqual(mailbox_list.mailboxes[1].addr_spec,
+                        'dinsdale@test.example.com')
+        self.assertEqual(mailbox_list.mailboxes,
+                         mailbox_list.all_mailboxes)
+
+    def test_get_mailbox_list_two_name_addr(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            ('"Roy A. Bear" <dinsdale@example.com>,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            [],
+            '')
+        self.assertEqual(len(mailbox_list.mailboxes), 2)
+        self.assertEqual(mailbox_list.mailboxes[0].addr_spec,
+                        'dinsdale@example.com')
+        self.assertEqual(mailbox_list.mailboxes[0].display_name,
+                        'Roy A. Bear')
+        self.assertEqual(mailbox_list.mailboxes[1].addr_spec,
+                        'dinsdale@test.example.com')
+        self.assertEqual(mailbox_list.mailboxes[1].display_name,
+                        'Fred Flintstone')
+        self.assertEqual(mailbox_list.mailboxes,
+                         mailbox_list.all_mailboxes)
+
+    def test_get_mailbox_list_two_complex(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            ('(foo) "Roy A. Bear" <dinsdale@example.com>(bar),'
+                ' "Fred Flintstone" <dinsdale@test.(bird)example.com>'),
+            ('(foo) "Roy A. Bear" <dinsdale@example.com>(bar),'
+                ' "Fred Flintstone" <dinsdale@test.(bird)example.com>'),
+            (' "Roy A. Bear" <dinsdale@example.com> ,'
+                ' "Fred Flintstone" <dinsdale@test. example.com>'),
+            [errors.ObsoleteHeaderDefect],
+            '')
+        self.assertEqual(len(mailbox_list.mailboxes), 2)
+        self.assertEqual(mailbox_list.mailboxes[0].addr_spec,
+                        'dinsdale@example.com')
+        self.assertEqual(mailbox_list.mailboxes[0].display_name,
+                        'Roy A. Bear')
+        self.assertEqual(mailbox_list.mailboxes[1].addr_spec,
+                        'dinsdale@test.example.com')
+        self.assertEqual(mailbox_list.mailboxes[1].display_name,
+                        'Fred Flintstone')
+        self.assertEqual(mailbox_list.mailboxes,
+                         mailbox_list.all_mailboxes)
+
+    def test_get_mailbox_list_unparseable_mailbox_null(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            ('"Roy A. Bear"[] dinsdale@example.com,'
+                ' "Fred Flintstone" <dinsdale@test.(bird)example.com>'),
+            ('"Roy A. Bear"[] dinsdale@example.com,'
+                ' "Fred Flintstone" <dinsdale@test.(bird)example.com>'),
+            ('"Roy A. Bear"[] dinsdale@example.com,'
+                ' "Fred Flintstone" <dinsdale@test. example.com>'),
+            [errors.InvalidHeaderDefect,   # the 'extra' text after the local part
+             errors.InvalidHeaderDefect,   # the local part with no angle-addr
+             errors.ObsoleteHeaderDefect,  # period in extra text (example.com)
+             errors.ObsoleteHeaderDefect], # (bird) in valid address.
+            '')
+        self.assertEqual(len(mailbox_list.mailboxes), 1)
+        self.assertEqual(len(mailbox_list.all_mailboxes), 2)
+        self.assertEqual(mailbox_list.all_mailboxes[0].token_type,
+                        'invalid-mailbox')
+        self.assertIsNone(mailbox_list.all_mailboxes[0].display_name)
+        self.assertEqual(mailbox_list.all_mailboxes[0].local_part,
+                        'Roy A. Bear')
+        self.assertIsNone(mailbox_list.all_mailboxes[0].domain)
+        self.assertEqual(mailbox_list.all_mailboxes[0].addr_spec,
+                        '"Roy A. Bear"')
+        self.assertIs(mailbox_list.all_mailboxes[1],
+                        mailbox_list.mailboxes[0])
+        self.assertEqual(mailbox_list.mailboxes[0].addr_spec,
+                        'dinsdale@test.example.com')
+        self.assertEqual(mailbox_list.mailboxes[0].display_name,
+                        'Fred Flintstone')
+
+    def test_get_mailbox_list_junk_after_valid_address(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            ('"Roy A. Bear" <dinsdale@example.com>@@,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>@@,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>@@,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            [errors.InvalidHeaderDefect],
+            '')
+        self.assertEqual(len(mailbox_list.mailboxes), 1)
+        self.assertEqual(len(mailbox_list.all_mailboxes), 2)
+        self.assertEqual(mailbox_list.all_mailboxes[0].addr_spec,
+                        'dinsdale@example.com')
+        self.assertEqual(mailbox_list.all_mailboxes[0].display_name,
+                        'Roy A. Bear')
+        self.assertEqual(mailbox_list.all_mailboxes[0].token_type,
+                        'invalid-mailbox')
+        self.assertIs(mailbox_list.all_mailboxes[1],
+                        mailbox_list.mailboxes[0])
+        self.assertEqual(mailbox_list.mailboxes[0].addr_spec,
+                        'dinsdale@test.example.com')
+        self.assertEqual(mailbox_list.mailboxes[0].display_name,
+                        'Fred Flintstone')
+
+    def test_get_mailbox_list_empty_list_element(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            ('"Roy A. Bear" <dinsdale@example.com>, (bird),,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>, (bird),,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>, ,,'
+                ' "Fred Flintstone" <dinsdale@test.example.com>'),
+            [errors.ObsoleteHeaderDefect]*2,
+            '')
+        self.assertEqual(len(mailbox_list.mailboxes), 2)
+        self.assertEqual(mailbox_list.all_mailboxes,
+                         mailbox_list.mailboxes)
+        self.assertEqual(mailbox_list.all_mailboxes[0].addr_spec,
+                        'dinsdale@example.com')
+        self.assertEqual(mailbox_list.all_mailboxes[0].display_name,
+                        'Roy A. Bear')
+        self.assertEqual(mailbox_list.mailboxes[1].addr_spec,
+                        'dinsdale@test.example.com')
+        self.assertEqual(mailbox_list.mailboxes[1].display_name,
+                        'Fred Flintstone')
+
+    def test_get_mailbox_list_only_empty_elements(self):
+        mailbox_list = self._test_get_x(parser.get_mailbox_list,
+            '(foo),, (bar)',
+            '(foo),, (bar)',
+            ' ,, ',
+            [errors.ObsoleteHeaderDefect]*3,
+            '')
+        self.assertEqual(len(mailbox_list.mailboxes), 0)
+        self.assertEqual(mailbox_list.all_mailboxes,
+                         mailbox_list.mailboxes)
+
+    # get_group_list
+
+    def test_get_group_list_cfws_only(self):
+        group_list = self._test_get_x(parser.get_group_list,
+            '(hidden);',
+            '(hidden)',
+            ' ',
+            [],
+            ';')
+        self.assertEqual(group_list.token_type, 'group-list')
+        self.assertEqual(len(group_list.mailboxes), 0)
+        self.assertEqual(group_list.mailboxes,
+                         group_list.all_mailboxes)
+
+    def test_get_group_list_mailbox_list(self):
+        group_list = self._test_get_x(parser.get_group_list,
+            'dinsdale@example.org, "Fred A. Bear" <dinsdale@example.org>',
+            'dinsdale@example.org, "Fred A. Bear" <dinsdale@example.org>',
+            'dinsdale@example.org, "Fred A. Bear" <dinsdale@example.org>',
+            [],
+            '')
+        self.assertEqual(group_list.token_type, 'group-list')
+        self.assertEqual(len(group_list.mailboxes), 2)
+        self.assertEqual(group_list.mailboxes,
+                         group_list.all_mailboxes)
+        self.assertEqual(group_list.mailboxes[1].display_name,
+                         'Fred A. Bear')
+
+    def test_get_group_list_obs_group_list(self):
+        group_list = self._test_get_x(parser.get_group_list,
+            ', (foo),,(bar)',
+            ', (foo),,(bar)',
+            ', ,, ',
+            [errors.ObsoleteHeaderDefect],
+            '')
+        self.assertEqual(group_list.token_type, 'group-list')
+        self.assertEqual(len(group_list.mailboxes), 0)
+        self.assertEqual(group_list.mailboxes,
+                         group_list.all_mailboxes)
+
+    def test_get_group_list_comment_only_invalid(self):
+        group_list = self._test_get_x(parser.get_group_list,
+            '(bar)',
+            '(bar)',
+            ' ',
+            [errors.InvalidHeaderDefect],
+            '')
+        self.assertEqual(group_list.token_type, 'group-list')
+        self.assertEqual(len(group_list.mailboxes), 0)
+        self.assertEqual(group_list.mailboxes,
+                         group_list.all_mailboxes)
+
+    # get_group
+
+    def test_get_group_empty(self):
+        group = self._test_get_x(parser.get_group,
+            'Monty Python:;',
+            'Monty Python:;',
+            'Monty Python:;',
+            [],
+            '')
+        self.assertEqual(group.token_type, 'group')
+        self.assertEqual(group.display_name, 'Monty Python')
+        self.assertEqual(len(group.mailboxes), 0)
+        self.assertEqual(group.mailboxes,
+                         group.all_mailboxes)
+
+    def test_get_troup_null_addr_spec(self):
+        group = self._test_get_x(parser.get_group,
+            'foo: <>;',
+            'foo: <>;',
+            'foo: <>;',
+            [errors.InvalidHeaderDefect],
+            '')
+        self.assertEqual(group.display_name, 'foo')
+        self.assertEqual(len(group.mailboxes), 0)
+        self.assertEqual(len(group.all_mailboxes), 1)
+        self.assertEqual(group.all_mailboxes[0].value, '<>')
+
+    def test_get_group_cfws_only(self):
+        group = self._test_get_x(parser.get_group,
+            'Monty Python: (hidden);',
+            'Monty Python: (hidden);',
+            'Monty Python: ;',
+            [],
+            '')
+        self.assertEqual(group.token_type, 'group')
+        self.assertEqual(group.display_name, 'Monty Python')
+        self.assertEqual(len(group.mailboxes), 0)
+        self.assertEqual(group.mailboxes,
+                         group.all_mailboxes)
+
+    def test_get_group_single_mailbox(self):
+        group = self._test_get_x(parser.get_group,
+            'Monty Python: "Fred A. Bear" <dinsdale@example.com>;',
+            'Monty Python: "Fred A. Bear" <dinsdale@example.com>;',
+            'Monty Python: "Fred A. Bear" <dinsdale@example.com>;',
+            [],
+            '')
+        self.assertEqual(group.token_type, 'group')
+        self.assertEqual(group.display_name, 'Monty Python')
+        self.assertEqual(len(group.mailboxes), 1)
+        self.assertEqual(group.mailboxes,
+                         group.all_mailboxes)
+        self.assertEqual(group.mailboxes[0].addr_spec,
+                         'dinsdale@example.com')
+
+    def test_get_group_mixed_list(self):
+        group = self._test_get_x(parser.get_group,
+            ('Monty Python: "Fred A. Bear" <dinsdale@example.com>,'
+                '(foo) Roger <ping@exampele.com>, x@test.example.com;'),
+            ('Monty Python: "Fred A. Bear" <dinsdale@example.com>,'
+                '(foo) Roger <ping@exampele.com>, x@test.example.com;'),
+            ('Monty Python: "Fred A. Bear" <dinsdale@example.com>,'
+                ' Roger <ping@exampele.com>, x@test.example.com;'),
+            [],
+            '')
+        self.assertEqual(group.token_type, 'group')
+        self.assertEqual(group.display_name, 'Monty Python')
+        self.assertEqual(len(group.mailboxes), 3)
+        self.assertEqual(group.mailboxes,
+                         group.all_mailboxes)
+        self.assertEqual(group.mailboxes[0].display_name,
+                         'Fred A. Bear')
+        self.assertEqual(group.mailboxes[1].display_name,
+                         'Roger')
+        self.assertEqual(group.mailboxes[2].local_part, 'x')
+
+    def test_get_group_one_invalid(self):
+        group = self._test_get_x(parser.get_group,
+            ('Monty Python: "Fred A. Bear" <dinsdale@example.com>,'
+                '(foo) Roger ping@exampele.com, x@test.example.com;'),
+            ('Monty Python: "Fred A. Bear" <dinsdale@example.com>,'
+                '(foo) Roger ping@exampele.com, x@test.example.com;'),
+            ('Monty Python: "Fred A. Bear" <dinsdale@example.com>,'
+                ' Roger ping@exampele.com, x@test.example.com;'),
+            [errors.InvalidHeaderDefect,   # non-angle addr makes local part invalid
+             errors.InvalidHeaderDefect],   # and its not obs-local either: no dots.
+            '')
+        self.assertEqual(group.token_type, 'group')
+        self.assertEqual(group.display_name, 'Monty Python')
+        self.assertEqual(len(group.mailboxes), 2)
+        self.assertEqual(len(group.all_mailboxes), 3)
+        self.assertEqual(group.mailboxes[0].display_name,
+                         'Fred A. Bear')
+        self.assertEqual(group.mailboxes[1].local_part, 'x')
+        self.assertIsNone(group.all_mailboxes[1].display_name)
+
+    # get_address
+
+    def test_get_address_simple(self):
+        address = self._test_get_x(parser.get_address,
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            [],
+            '')
+        self.assertEqual(address.token_type, 'address')
+        self.assertEqual(len(address.mailboxes), 1)
+        self.assertEqual(address.mailboxes,
+                         address.all_mailboxes)
+        self.assertEqual(address.mailboxes[0].domain,
+                         'example.com')
+        self.assertEqual(address[0].token_type,
+                         'mailbox')
+
+    def test_get_address_complex(self):
+        address = self._test_get_x(parser.get_address,
+            '(foo) "Fred A. Bear" <(bird)dinsdale@example.com>',
+            '(foo) "Fred A. Bear" <(bird)dinsdale@example.com>',
+            ' "Fred A. Bear" < dinsdale@example.com>',
+            [],
+            '')
+        self.assertEqual(address.token_type, 'address')
+        self.assertEqual(len(address.mailboxes), 1)
+        self.assertEqual(address.mailboxes,
+                         address.all_mailboxes)
+        self.assertEqual(address.mailboxes[0].display_name,
+                         'Fred A. Bear')
+        self.assertEqual(address[0].token_type,
+                         'mailbox')
+
+    def test_get_address_empty_group(self):
+        address = self._test_get_x(parser.get_address,
+            'Monty Python:;',
+            'Monty Python:;',
+            'Monty Python:;',
+            [],
+            '')
+        self.assertEqual(address.token_type, 'address')
+        self.assertEqual(len(address.mailboxes), 0)
+        self.assertEqual(address.mailboxes,
+                         address.all_mailboxes)
+        self.assertEqual(address[0].token_type,
+                         'group')
+        self.assertEqual(address[0].display_name,
+                         'Monty Python')
+
+    def test_get_address_group(self):
+        address = self._test_get_x(parser.get_address,
+            'Monty Python: x@example.com, y@example.com;',
+            'Monty Python: x@example.com, y@example.com;',
+            'Monty Python: x@example.com, y@example.com;',
+            [],
+            '')
+        self.assertEqual(address.token_type, 'address')
+        self.assertEqual(len(address.mailboxes), 2)
+        self.assertEqual(address.mailboxes,
+                         address.all_mailboxes)
+        self.assertEqual(address[0].token_type,
+                         'group')
+        self.assertEqual(address[0].display_name,
+                         'Monty Python')
+        self.assertEqual(address.mailboxes[0].local_part, 'x')
+
+    def test_get_address_quoted_local_part(self):
+        address = self._test_get_x(parser.get_address,
+            '"foo bar"@example.com',
+            '"foo bar"@example.com',
+            '"foo bar"@example.com',
+            [],
+            '')
+        self.assertEqual(address.token_type, 'address')
+        self.assertEqual(len(address.mailboxes), 1)
+        self.assertEqual(address.mailboxes,
+                         address.all_mailboxes)
+        self.assertEqual(address.mailboxes[0].domain,
+                         'example.com')
+        self.assertEqual(address.mailboxes[0].local_part,
+                         'foo bar')
+        self.assertEqual(address[0].token_type, 'mailbox')
+
+    def test_get_address_ends_at_special(self):
+        address = self._test_get_x(parser.get_address,
+            'dinsdale@example.com, next',
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            [],
+            ', next')
+        self.assertEqual(address.token_type, 'address')
+        self.assertEqual(len(address.mailboxes), 1)
+        self.assertEqual(address.mailboxes,
+                         address.all_mailboxes)
+        self.assertEqual(address.mailboxes[0].domain,
+                         'example.com')
+        self.assertEqual(address[0].token_type, 'mailbox')
+
+    def test_get_address_invalid_mailbox_invalid(self):
+        address = self._test_get_x(parser.get_address,
+            'ping example.com, next',
+            'ping example.com',
+            'ping example.com',
+            [errors.InvalidHeaderDefect,    # addr-spec with no domain
+             errors.InvalidHeaderDefect,    # invalid local-part
+             errors.InvalidHeaderDefect,    # missing .s in local-part
+            ],
+            ', next')
+        self.assertEqual(address.token_type, 'address')
+        self.assertEqual(len(address.mailboxes), 0)
+        self.assertEqual(len(address.all_mailboxes), 1)
+        self.assertIsNone(address.all_mailboxes[0].domain)
+        self.assertEqual(address.all_mailboxes[0].local_part, 'ping example.com')
+        self.assertEqual(address[0].token_type, 'invalid-mailbox')
+
+    def test_get_address_quoted_strings_in_atom_list(self):
+        address = self._test_get_x(parser.get_address,
+            '""example" example"@example.com',
+            '""example" example"@example.com',
+            'example example@example.com',
+            [errors.InvalidHeaderDefect]*3,
+            '')
+        self.assertEqual(address.all_mailboxes[0].local_part, 'example example')
+        self.assertEqual(address.all_mailboxes[0].domain, 'example.com')
+        self.assertEqual(address.all_mailboxes[0].addr_spec, '"example example"@example.com')
+
+
+    # get_address_list
+
+    def test_get_address_list_mailboxes_simple(self):
+        address_list = self._test_get_x(parser.get_address_list,
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            'dinsdale@example.com',
+            [],
+            '')
+        self.assertEqual(address_list.token_type, 'address-list')
+        self.assertEqual(len(address_list.mailboxes), 1)
+        self.assertEqual(address_list.mailboxes,
+                         address_list.all_mailboxes)
+        self.assertEqual([str(x) for x in address_list.mailboxes],
+                         [str(x) for x in address_list.addresses])
+        self.assertEqual(address_list.mailboxes[0].domain, 'example.com')
+        self.assertEqual(address_list[0].token_type, 'address')
+        self.assertIsNone(address_list[0].display_name)
+
+    def test_get_address_list_mailboxes_two_simple(self):
+        address_list = self._test_get_x(parser.get_address_list,
+            'foo@example.com, "Fred A. Bar" <bar@example.com>',
+            'foo@example.com, "Fred A. Bar" <bar@example.com>',
+            'foo@example.com, "Fred A. Bar" <bar@example.com>',
+            [],
+            '')
+        self.assertEqual(address_list.token_type, 'address-list')
+        self.assertEqual(len(address_list.mailboxes), 2)
+        self.assertEqual(address_list.mailboxes,
+                         address_list.all_mailboxes)
+        self.assertEqual([str(x) for x in address_list.mailboxes],
+                         [str(x) for x in address_list.addresses])
+        self.assertEqual(address_list.mailboxes[0].local_part, 'foo')
+        self.assertEqual(address_list.mailboxes[1].display_name, "Fred A. Bar")
+
+    def test_get_address_list_mailboxes_complex(self):
+        address_list = self._test_get_x(parser.get_address_list,
+            ('"Roy A. Bear" <dinsdale@example.com>, '
+                '(ping) Foo <x@example.com>,'
+                'Nobody Is. Special <y@(bird)example.(bad)com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>, '
+                '(ping) Foo <x@example.com>,'
+                'Nobody Is. Special <y@(bird)example.(bad)com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>, '
+                'Foo <x@example.com>,'
+                '"Nobody Is. Special" <y@example. com>'),
+            [errors.ObsoleteHeaderDefect, # period in Is.
+            errors.ObsoleteHeaderDefect], # cfws in domain
+            '')
+        self.assertEqual(address_list.token_type, 'address-list')
+        self.assertEqual(len(address_list.mailboxes), 3)
+        self.assertEqual(address_list.mailboxes,
+                         address_list.all_mailboxes)
+        self.assertEqual([str(x) for x in address_list.mailboxes],
+                         [str(x) for x in address_list.addresses])
+        self.assertEqual(address_list.mailboxes[0].domain, 'example.com')
+        self.assertEqual(address_list.mailboxes[0].token_type, 'mailbox')
+        self.assertEqual(address_list.addresses[0].token_type, 'address')
+        self.assertEqual(address_list.mailboxes[1].local_part, 'x')
+        self.assertEqual(address_list.mailboxes[2].display_name,
+                         'Nobody Is. Special')
+
+    def test_get_address_list_mailboxes_invalid_addresses(self):
+        address_list = self._test_get_x(parser.get_address_list,
+            ('"Roy A. Bear" <dinsdale@example.com>, '
+                '(ping) Foo x@example.com[],'
+                'Nobody Is. Special <(bird)example.(bad)com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>, '
+                '(ping) Foo x@example.com[],'
+                'Nobody Is. Special <(bird)example.(bad)com>'),
+            ('"Roy A. Bear" <dinsdale@example.com>, '
+                'Foo x@example.com[],'
+                '"Nobody Is. Special" < example. com>'),
+             [errors.InvalidHeaderDefect,   # invalid address in list
+              errors.InvalidHeaderDefect,   # 'Foo x' local part invalid.
+              errors.InvalidHeaderDefect,   # Missing . in 'Foo x' local part
+              errors.ObsoleteHeaderDefect,  # period in 'Is.' disp-name phrase
+              errors.InvalidHeaderDefect,   # no domain part in addr-spec
+              errors.ObsoleteHeaderDefect], # addr-spec has comment in it
+            '')
+        self.assertEqual(address_list.token_type, 'address-list')
+        self.assertEqual(len(address_list.mailboxes), 1)
+        self.assertEqual(len(address_list.all_mailboxes), 3)
+        self.assertEqual([str(x) for x in address_list.all_mailboxes],
+                         [str(x) for x in address_list.addresses])
+        self.assertEqual(address_list.mailboxes[0].domain, 'example.com')
+        self.assertEqual(address_list.mailboxes[0].token_type, 'mailbox')
+        self.assertEqual(address_list.addresses[0].token_type, 'address')
+        self.assertEqual(address_list.addresses[1].token_type, 'address')
+        self.assertEqual(len(address_list.addresses[0].mailboxes), 1)
+        self.assertEqual(len(address_list.addresses[1].mailboxes), 0)
+        self.assertEqual(len(address_list.addresses[1].mailboxes), 0)
+        self.assertEqual(
+            address_list.addresses[1].all_mailboxes[0].local_part, 'Foo x')
+        self.assertEqual(
+            address_list.addresses[2].all_mailboxes[0].display_name,
+                "Nobody Is. Special")
+
+    def test_get_address_list_group_empty(self):
+        address_list = self._test_get_x(parser.get_address_list,
+            'Monty Python: ;',
+            'Monty Python: ;',
+            'Monty Python: ;',
+            [],
+            '')
+        self.assertEqual(address_list.token_type, 'address-list')
+        self.assertEqual(len(address_list.mailboxes), 0)
+        self.assertEqual(address_list.mailboxes,
+                         address_list.all_mailboxes)
+        self.assertEqual(len(address_list.addresses), 1)
+        self.assertEqual(address_list.addresses[0].token_type, 'address')
+        self.assertEqual(address_list.addresses[0].display_name, 'Monty Python')
+        self.assertEqual(len(address_list.addresses[0].mailboxes), 0)
+
+    def test_get_address_list_group_simple(self):
+        address_list = self._test_get_x(parser.get_address_list,
+            'Monty Python: dinsdale@example.com;',
+            'Monty Python: dinsdale@example.com;',
+            'Monty Python: dinsdale@example.com;',
+            [],
+            '')
+        self.assertEqual(address_list.token_type, 'address-list')
+        self.assertEqual(len(address_list.mailboxes), 1)
+        self.assertEqual(address_list.mailboxes,
+                         address_list.all_mailboxes)
+        self.assertEqual(address_list.mailboxes[0].domain, 'example.com')
+        self.assertEqual(address_list.addresses[0].display_name,
+                         'Monty Python')
+        self.assertEqual(address_list.addresses[0].mailboxes[0].domain,
+                         'example.com')
+
+    def test_get_address_list_group_and_mailboxes(self):
+        address_list = self._test_get_x(parser.get_address_list,
+            ('Monty Python: dinsdale@example.com, "Fred" <flint@example.com>;, '
+                'Abe <x@example.com>, Bee <y@example.com>'),
+            ('Monty Python: dinsdale@example.com, "Fred" <flint@example.com>;, '
+                'Abe <x@example.com>, Bee <y@example.com>'),
+            ('Monty Python: dinsdale@example.com, "Fred" <flint@example.com>;, '
+                'Abe <x@example.com>, Bee <y@example.com>'),
+            [],
+            '')
+        self.assertEqual(address_list.token_type, 'address-list')
+        self.assertEqual(len(address_list.mailboxes), 4)
+        self.assertEqual(address_list.mailboxes,
+                         address_list.all_mailboxes)
+        self.assertEqual(len(address_list.addresses), 3)
+        self.assertEqual(address_list.mailboxes[0].local_part, 'dinsdale')
+        self.assertEqual(address_list.addresses[0].display_name,
+                         'Monty Python')
+        self.assertEqual(address_list.addresses[0].mailboxes[0].domain,
+                         'example.com')
+        self.assertEqual(address_list.addresses[0].mailboxes[1].local_part,
+                         'flint')
+        self.assertEqual(address_list.addresses[1].mailboxes[0].local_part,
+                         'x')
+        self.assertEqual(address_list.addresses[2].mailboxes[0].local_part,
+                         'y')
+        self.assertEqual(str(address_list.addresses[1]),
+                         str(address_list.mailboxes[2]))
+
+
+class TestFolding(TestEmailBase):
+
+    policy = policy.default
+
+    def _test(self, tl, folded, policy=policy):
+        self.assertEqual(tl.fold(policy=policy), folded, tl.ppstr())
+
+    def test_simple_unstructured_no_folds(self):
+        self._test(parser.get_unstructured("This is a test"),
+                   "This is a test\n")
+
+    def test_simple_unstructured_folded(self):
+        self._test(parser.get_unstructured("This is also a test, but this "
+                        "time there are enough words (and even some "
+                        "symbols) to make it wrap; at least in theory."),
+                   "This is also a test, but this time there are enough "
+                        "words (and even some\n"
+                   " symbols) to make it wrap; at least in theory.\n")
+
+    def test_unstructured_with_unicode_no_folds(self):
+        self._test(parser.get_unstructured("hübsch kleiner beißt"),
+                   "=?utf-8?q?h=C3=BCbsch_kleiner_bei=C3=9Ft?=\n")
+
+    def test_one_ew_on_each_of_two_wrapped_lines(self):
+        self._test(parser.get_unstructured("Mein kleiner Kaktus ist sehr "
+                                           "hübsch.  Es hat viele Stacheln "
+                                           "und oft beißt mich."),
+                   "Mein kleiner Kaktus ist sehr =?utf-8?q?h=C3=BCbsch=2E?=  "
+                        "Es hat viele Stacheln\n"
+                   " und oft =?utf-8?q?bei=C3=9Ft?= mich.\n")
+
+    def test_ews_combined_before_wrap(self):
+        self._test(parser.get_unstructured("Mein Kaktus ist hübsch.  "
+                                           "Es beißt mich.  "
+                                           "And that's all I'm sayin."),
+                   "Mein Kaktus ist =?utf-8?q?h=C3=BCbsch=2E__Es_bei=C3=9Ft?= "
+                        "mich.  And that's\n"
+                   " all I'm sayin.\n")
+
+    # XXX Need test of an encoded word so long that it needs to be wrapped
+
+    def test_simple_address(self):
+        self._test(parser.get_address_list("abc <xyz@example.com>")[0],
+                   "abc <xyz@example.com>\n")
+
+    def test_address_list_folding_at_commas(self):
+        self._test(parser.get_address_list('abc <xyz@example.com>, '
+                                            '"Fred Blunt" <sharp@example.com>, '
+                                            '"J.P.Cool" <hot@example.com>, '
+                                            '"K<>y" <key@example.com>, '
+                                            'Firesale <cheap@example.com>, '
+                                            '<end@example.com>')[0],
+                    'abc <xyz@example.com>, "Fred Blunt" <sharp@example.com>,\n'
+                    ' "J.P.Cool" <hot@example.com>, "K<>y" <key@example.com>,\n'
+                    ' Firesale <cheap@example.com>, <end@example.com>\n')
+
+    def test_address_list_with_unicode_names(self):
+        self._test(parser.get_address_list(
+            'Hübsch Kaktus <beautiful@example.com>, '
+                'beißt beißt <biter@example.com>')[0],
+            '=?utf-8?q?H=C3=BCbsch?= Kaktus <beautiful@example.com>,\n'
+                ' =?utf-8?q?bei=C3=9Ft_bei=C3=9Ft?= <biter@example.com>\n')
+
+    def test_address_list_with_unicode_names_in_quotes(self):
+        self._test(parser.get_address_list(
+            '"Hübsch Kaktus" <beautiful@example.com>, '
+                '"beißt" beißt <biter@example.com>')[0],
+            '=?utf-8?q?H=C3=BCbsch?= Kaktus <beautiful@example.com>,\n'
+                ' =?utf-8?q?bei=C3=9Ft_bei=C3=9Ft?= <biter@example.com>\n')
+
+    # XXX Need tests with comments on various sides of a unicode token,
+    # and with unicode tokens in the comments.  Spaces inside the quotes
+    # currently don't do the right thing.
+
+    def test_initial_whitespace_splitting(self):
+        body = parser.get_unstructured('   ' + 'x'*77)
+        header = parser.Header([
+            parser.HeaderLabel([parser.ValueTerminal('test:', 'atext')]),
+            parser.CFWSList([parser.WhiteSpaceTerminal(' ', 'fws')]), body])
+        self._test(header, 'test:   \n ' + 'x'*77 + '\n')
+
+    def test_whitespace_splitting(self):
+        self._test(parser.get_unstructured('xxx   ' + 'y'*77),
+                   'xxx  \n ' + 'y'*77 + '\n')
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/Lib/test/test_email/test__headerregistry.py b/Lib/test/test_email/test__headerregistry.py
new file mode 100644
index 0000000..4398e29
--- /dev/null
+++ b/Lib/test/test_email/test__headerregistry.py
@@ -0,0 +1,717 @@
+import datetime
+import textwrap
+import unittest
+from email import errors
+from email import policy
+from test.test_email import TestEmailBase
+from email import _headerregistry
+# Address and Group are public but I'm not sure where to put them yet.
+from email._headerregistry import Address, Group
+
+
+class TestHeaderRegistry(TestEmailBase):
+
+    def test_arbitrary_name_unstructured(self):
+        factory = _headerregistry.HeaderRegistry()
+        h = factory('foobar', 'test')
+        self.assertIsInstance(h, _headerregistry.BaseHeader)
+        self.assertIsInstance(h, _headerregistry.UnstructuredHeader)
+
+    def test_name_case_ignored(self):
+        factory = _headerregistry.HeaderRegistry()
+        # Whitebox check that test is valid
+        self.assertNotIn('Subject', factory.registry)
+        h = factory('Subject', 'test')
+        self.assertIsInstance(h, _headerregistry.BaseHeader)
+        self.assertIsInstance(h, _headerregistry.UniqueUnstructuredHeader)
+
+    class FooBase:
+        def __init__(self, *args, **kw):
+            pass
+
+    def test_override_default_base_class(self):
+        factory = _headerregistry.HeaderRegistry(base_class=self.FooBase)
+        h = factory('foobar', 'test')
+        self.assertIsInstance(h, self.FooBase)
+        self.assertIsInstance(h, _headerregistry.UnstructuredHeader)
+
+    class FooDefault:
+        parse = _headerregistry.UnstructuredHeader.parse
+
+    def test_override_default_class(self):
+        factory = _headerregistry.HeaderRegistry(default_class=self.FooDefault)
+        h = factory('foobar', 'test')
+        self.assertIsInstance(h, _headerregistry.BaseHeader)
+        self.assertIsInstance(h, self.FooDefault)
+
+    def test_override_default_class_only_overrides_default(self):
+        factory = _headerregistry.HeaderRegistry(default_class=self.FooDefault)
+        h = factory('subject', 'test')
+        self.assertIsInstance(h, _headerregistry.BaseHeader)
+        self.assertIsInstance(h, _headerregistry.UniqueUnstructuredHeader)
+
+    def test_dont_use_default_map(self):
+        factory = _headerregistry.HeaderRegistry(use_default_map=False)
+        h = factory('subject', 'test')
+        self.assertIsInstance(h, _headerregistry.BaseHeader)
+        self.assertIsInstance(h, _headerregistry.UnstructuredHeader)
+
+    def test_map_to_type(self):
+        factory = _headerregistry.HeaderRegistry()
+        h1 = factory('foobar', 'test')
+        factory.map_to_type('foobar', _headerregistry.UniqueUnstructuredHeader)
+        h2 = factory('foobar', 'test')
+        self.assertIsInstance(h1, _headerregistry.BaseHeader)
+        self.assertIsInstance(h1, _headerregistry.UnstructuredHeader)
+        self.assertIsInstance(h2, _headerregistry.BaseHeader)
+        self.assertIsInstance(h2, _headerregistry.UniqueUnstructuredHeader)
+
+
+class TestHeaderBase(TestEmailBase):
+
+    factory = _headerregistry.HeaderRegistry()
+
+    def make_header(self, name, value):
+        return self.factory(name, value)
+
+
+class TestBaseHeaderFeatures(TestHeaderBase):
+
+    def test_str(self):
+        h = self.make_header('subject', 'this is a test')
+        self.assertIsInstance(h, str)
+        self.assertEqual(h, 'this is a test')
+        self.assertEqual(str(h), 'this is a test')
+
+    def test_substr(self):
+        h = self.make_header('subject', 'this is a test')
+        self.assertEqual(h[5:7], 'is')
+
+    def test_has_name(self):
+        h = self.make_header('subject', 'this is a test')
+        self.assertEqual(h.name, 'subject')
+
+    def _test_attr_ro(self, attr):
+        h = self.make_header('subject', 'this is a test')
+        with self.assertRaises(AttributeError):
+            setattr(h, attr, 'foo')
+
+    def test_name_read_only(self):
+        self._test_attr_ro('name')
+
+    def test_defects_read_only(self):
+        self._test_attr_ro('defects')
+
+    def test_defects_is_tuple(self):
+        h = self.make_header('subject', 'this is a test')
+        self.assertEqual(len(h.defects), 0)
+        self.assertIsInstance(h.defects, tuple)
+        # Make sure it is still true when there are defects.
+        h = self.make_header('date', '')
+        self.assertEqual(len(h.defects), 1)
+        self.assertIsInstance(h.defects, tuple)
+
+    # XXX: FIXME
+    #def test_CR_in_value(self):
+    #    # XXX: this also re-raises the issue of embedded headers,
+    #    # need test and solution for that.
+    #    value = '\r'.join(['this is', ' a test'])
+    #    h = self.make_header('subject', value)
+    #    self.assertEqual(h, value)
+    #    self.assertDefectsEqual(h.defects, [errors.ObsoleteHeaderDefect])
+
+    def test_RFC2047_value_decoded(self):
+        value = '=?utf-8?q?this_is_a_test?='
+        h = self.make_header('subject', value)
+        self.assertEqual(h, 'this is a test')
+
+
+class TestDateHeader(TestHeaderBase):
+
+    datestring = 'Sun, 23 Sep 2001 20:10:55 -0700'
+    utcoffset = datetime.timedelta(hours=-7)
+    tz = datetime.timezone(utcoffset)
+    dt = datetime.datetime(2001, 9, 23, 20, 10, 55, tzinfo=tz)
+
+    def test_parse_date(self):
+        h = self.make_header('date', self.datestring)
+        self.assertEqual(h, self.datestring)
+        self.assertEqual(h.datetime, self.dt)
+        self.assertEqual(h.datetime.utcoffset(), self.utcoffset)
+        self.assertEqual(h.defects, ())
+
+    def test_set_from_datetime(self):
+        h = self.make_header('date', self.dt)
+        self.assertEqual(h, self.datestring)
+        self.assertEqual(h.datetime, self.dt)
+        self.assertEqual(h.defects, ())
+
+    def test_date_header_properties(self):
+        h = self.make_header('date', self.datestring)
+        self.assertIsInstance(h, _headerregistry.UniqueDateHeader)
+        self.assertEqual(h.max_count, 1)
+        self.assertEqual(h.defects, ())
+
+    def test_resent_date_header_properties(self):
+        h = self.make_header('resent-date', self.datestring)
+        self.assertIsInstance(h, _headerregistry.DateHeader)
+        self.assertEqual(h.max_count, None)
+        self.assertEqual(h.defects, ())
+
+    def test_no_value_is_defect(self):
+        h = self.make_header('date', '')
+        self.assertEqual(len(h.defects), 1)
+        self.assertIsInstance(h.defects[0], errors.HeaderMissingRequiredValue)
+
+    def test_datetime_read_only(self):
+        h = self.make_header('date', self.datestring)
+        with self.assertRaises(AttributeError):
+            h.datetime = 'foo'
+
+
+class TestAddressHeader(TestHeaderBase):
+
+    examples = {
+
+        'empty':
+            ('<>',
+             [errors.InvalidHeaderDefect],
+             '<>',
+             '',
+             '<>',
+             '',
+             '',
+             None),
+
+        'address_only':
+            ('zippy@pinhead.com',
+             [],
+             'zippy@pinhead.com',
+             '',
+             'zippy@pinhead.com',
+             'zippy',
+             'pinhead.com',
+             None),
+
+        'name_and_address':
+            ('Zaphrod Beblebrux <zippy@pinhead.com>',
+             [],
+             'Zaphrod Beblebrux <zippy@pinhead.com>',
+             'Zaphrod Beblebrux',
+             'zippy@pinhead.com',
+             'zippy',
+             'pinhead.com',
+             None),
+
+        'quoted_local_part':
+            ('Zaphrod Beblebrux <"foo bar"@pinhead.com>',
+             [],
+             'Zaphrod Beblebrux <"foo bar"@pinhead.com>',
+             'Zaphrod Beblebrux',
+             '"foo bar"@pinhead.com',
+             'foo bar',
+             'pinhead.com',
+             None),
+
+        'quoted_parens_in_name':
+            (r'"A \(Special\) Person" <person@dom.ain>',
+             [],
+             '"A (Special) Person" <person@dom.ain>',
+             'A (Special) Person',
+             'person@dom.ain',
+             'person',
+             'dom.ain',
+             None),
+
+        'quoted_backslashes_in_name':
+            (r'"Arthur \\Backslash\\ Foobar" <person@dom.ain>',
+             [],
+             r'"Arthur \\Backslash\\ Foobar" <person@dom.ain>',
+             r'Arthur \Backslash\ Foobar',
+             'person@dom.ain',
+             'person',
+             'dom.ain',
+             None),
+
+        'name_with_dot':
+            ('John X. Doe <jxd@example.com>',
+             [errors.ObsoleteHeaderDefect],
+             '"John X. Doe" <jxd@example.com>',
+             'John X. Doe',
+             'jxd@example.com',
+             'jxd',
+             'example.com',
+             None),
+
+        'quoted_strings_in_local_part':
+            ('""example" example"@example.com',
+             [errors.InvalidHeaderDefect]*3,
+             '"example example"@example.com',
+             '',
+             '"example example"@example.com',
+             'example example',
+             'example.com',
+             None),
+
+        'escaped_quoted_strings_in_local_part':
+            (r'"\"example\" example"@example.com',
+             [],
+             r'"\"example\" example"@example.com',
+             '',
+             r'"\"example\" example"@example.com',
+             r'"example" example',
+             'example.com',
+            None),
+
+        'escaped_escapes_in_local_part':
+            (r'"\\"example\\" example"@example.com',
+             [errors.InvalidHeaderDefect]*5,
+             r'"\\example\\\\ example"@example.com',
+             '',
+             r'"\\example\\\\ example"@example.com',
+             r'\example\\ example',
+             'example.com',
+            None),
+
+        'spaces_in_unquoted_local_part_collapsed':
+            ('merwok  wok  @example.com',
+             [errors.InvalidHeaderDefect]*2,
+             '"merwok wok"@example.com',
+             '',
+             '"merwok wok"@example.com',
+             'merwok wok',
+             'example.com',
+             None),
+
+        'spaces_around_dots_in_local_part_removed':
+            ('merwok. wok .  wok@example.com',
+             [errors.ObsoleteHeaderDefect],
+             'merwok.wok.wok@example.com',
+             '',
+             'merwok.wok.wok@example.com',
+             'merwok.wok.wok',
+             'example.com',
+             None),
+
+        }
+
+        # XXX: Need many more examples, and in particular some with names in
+        # trailing comments, which aren't currently handled.  comments in
+        # general are not handled yet.
+
+    def _test_single_addr(self, source, defects, decoded, display_name,
+                          addr_spec, username, domain, comment):
+        h = self.make_header('sender', source)
+        self.assertEqual(h, decoded)
+        self.assertDefectsEqual(h.defects, defects)
+        a = h.address
+        self.assertEqual(str(a), decoded)
+        self.assertEqual(len(h.groups), 1)
+        self.assertEqual([a], list(h.groups[0].addresses))
+        self.assertEqual([a], list(h.addresses))
+        self.assertEqual(a.display_name, display_name)
+        self.assertEqual(a.addr_spec, addr_spec)
+        self.assertEqual(a.username, username)
+        self.assertEqual(a.domain, domain)
+        # XXX: we have no comment support yet.
+        #self.assertEqual(a.comment, comment)
+
+    for name in examples:
+        locals()['test_'+name] = (
+            lambda self, name=name:
+                self._test_single_addr(*self.examples[name]))
+
+    def _test_group_single_addr(self, source, defects, decoded, display_name,
+                                addr_spec, username, domain, comment):
+        source = 'foo: {};'.format(source)
+        gdecoded = 'foo: {};'.format(decoded) if decoded else 'foo:;'
+        h = self.make_header('to', source)
+        self.assertEqual(h, gdecoded)
+        self.assertDefectsEqual(h.defects, defects)
+        self.assertEqual(h.groups[0].addresses, h.addresses)
+        self.assertEqual(len(h.groups), 1)
+        self.assertEqual(len(h.addresses), 1)
+        a = h.addresses[0]
+        self.assertEqual(str(a), decoded)
+        self.assertEqual(a.display_name, display_name)
+        self.assertEqual(a.addr_spec, addr_spec)
+        self.assertEqual(a.username, username)
+        self.assertEqual(a.domain, domain)
+
+    for name in examples:
+        locals()['test_group_'+name] = (
+            lambda self, name=name:
+                self._test_group_single_addr(*self.examples[name]))
+
+    def test_simple_address_list(self):
+        value = ('Fred <dinsdale@python.org>, foo@example.com, '
+                    '"Harry W. Hastings" <hasty@example.com>')
+        h = self.make_header('to', value)
+        self.assertEqual(h, value)
+        self.assertEqual(len(h.groups), 3)
+        self.assertEqual(len(h.addresses), 3)
+        for i in range(3):
+            self.assertEqual(h.groups[i].addresses[0], h.addresses[i])
+        self.assertEqual(str(h.addresses[0]), 'Fred <dinsdale@python.org>')
+        self.assertEqual(str(h.addresses[1]), 'foo@example.com')
+        self.assertEqual(str(h.addresses[2]),
+            '"Harry W. Hastings" <hasty@example.com>')
+        self.assertEqual(h.addresses[2].display_name,
+            'Harry W. Hastings')
+
+    def test_complex_address_list(self):
+        examples = list(self.examples.values())
+        source = ('dummy list:;, another: (empty);,' +
+                 ', '.join([x[0] for x in examples[:4]]) + ', ' +
+                 r'"A \"list\"": ' +
+                    ', '.join([x[0] for x in examples[4:6]]) + ';,' +
+                 ', '.join([x[0] for x in examples[6:]])
+            )
+        # XXX: the fact that (empty) disappears here is a potential API design
+        # bug.  We don't currently have a way to preserve comments.
+        expected = ('dummy list:;, another:;, ' +
+                 ', '.join([x[2] for x in examples[:4]]) + ', ' +
+                 r'"A \"list\"": ' +
+                    ', '.join([x[2] for x in examples[4:6]]) + ';, ' +
+                 ', '.join([x[2] for x in examples[6:]])
+            )
+
+        h = self.make_header('to', source)
+        self.assertEqual(h.split(','), expected.split(','))
+        self.assertEqual(h, expected)
+        self.assertEqual(len(h.groups), 7 + len(examples) - 6)
+        self.assertEqual(h.groups[0].display_name, 'dummy list')
+        self.assertEqual(h.groups[1].display_name, 'another')
+        self.assertEqual(h.groups[6].display_name, 'A "list"')
+        self.assertEqual(len(h.addresses), len(examples))
+        for i in range(4):
+            self.assertIsNone(h.groups[i+2].display_name)
+            self.assertEqual(str(h.groups[i+2].addresses[0]), examples[i][2])
+        for i in range(7, 7 + len(examples) - 6):
+            self.assertIsNone(h.groups[i].display_name)
+            self.assertEqual(str(h.groups[i].addresses[0]), examples[i-1][2])
+        for i in range(len(examples)):
+            self.assertEqual(str(h.addresses[i]), examples[i][2])
+            self.assertEqual(h.addresses[i].addr_spec, examples[i][4])
+
+    def test_address_read_only(self):
+        h = self.make_header('sender', 'abc@xyz.com')
+        with self.assertRaises(AttributeError):
+            h.address = 'foo'
+
+    def test_addresses_read_only(self):
+        h = self.make_header('sender', 'abc@xyz.com')
+        with self.assertRaises(AttributeError):
+            h.addresses = 'foo'
+
+    def test_groups_read_only(self):
+        h = self.make_header('sender', 'abc@xyz.com')
+        with self.assertRaises(AttributeError):
+            h.groups = 'foo'
+
+    def test_addresses_types(self):
+        source = 'me <who@example.com>'
+        h = self.make_header('to', source)
+        self.assertIsInstance(h.addresses, tuple)
+        self.assertIsInstance(h.addresses[0], Address)
+
+    def test_groups_types(self):
+        source = 'me <who@example.com>'
+        h = self.make_header('to', source)
+        self.assertIsInstance(h.groups, tuple)
+        self.assertIsInstance(h.groups[0], Group)
+
+    def test_set_from_Address(self):
+        h = self.make_header('to', Address('me', 'foo', 'example.com'))
+        self.assertEqual(h, 'me <foo@example.com>')
+
+    def test_set_from_Address_list(self):
+        h = self.make_header('to', [Address('me', 'foo', 'example.com'),
+                                    Address('you', 'bar', 'example.com')])
+        self.assertEqual(h, 'me <foo@example.com>, you <bar@example.com>')
+
+    def test_set_from_Address_and_Group_list(self):
+        h = self.make_header('to', [Address('me', 'foo', 'example.com'),
+                                    Group('bing', [Address('fiz', 'z', 'b.com'),
+                                                   Address('zif', 'f', 'c.com')]),
+                                    Address('you', 'bar', 'example.com')])
+        self.assertEqual(h, 'me <foo@example.com>, bing: fiz <z@b.com>, '
+                            'zif <f@c.com>;, you <bar@example.com>')
+        self.assertEqual(h.fold(policy=policy.default.clone(max_line_length=40)),
+                        'to: me <foo@example.com>,\n'
+                        ' bing: fiz <z@b.com>, zif <f@c.com>;,\n'
+                        ' you <bar@example.com>\n')
+
+    def test_set_from_Group_list(self):
+        h = self.make_header('to', [Group('bing', [Address('fiz', 'z', 'b.com'),
+                                                   Address('zif', 'f', 'c.com')])])
+        self.assertEqual(h, 'bing: fiz <z@b.com>, zif <f@c.com>;')
+
+
+class TestAddressAndGroup(TestEmailBase):
+
+    def _test_attr_ro(self, obj, attr):
+        with self.assertRaises(AttributeError):
+            setattr(obj, attr, 'foo')
+
+    def test_address_display_name_ro(self):
+        self._test_attr_ro(Address('foo', 'bar', 'baz'), 'display_name')
+
+    def test_address_username_ro(self):
+        self._test_attr_ro(Address('foo', 'bar', 'baz'), 'username')
+
+    def test_address_domain_ro(self):
+        self._test_attr_ro(Address('foo', 'bar', 'baz'), 'domain')
+
+    def test_group_display_name_ro(self):
+        self._test_attr_ro(Group('foo'), 'display_name')
+
+    def test_group_addresses_ro(self):
+        self._test_attr_ro(Group('foo'), 'addresses')
+
+    def test_address_from_username_domain(self):
+        a = Address('foo', 'bar', 'baz')
+        self.assertEqual(a.display_name, 'foo')
+        self.assertEqual(a.username, 'bar')
+        self.assertEqual(a.domain, 'baz')
+        self.assertEqual(a.addr_spec, 'bar@baz')
+        self.assertEqual(str(a), 'foo <bar@baz>')
+
+    def test_address_from_addr_spec(self):
+        a = Address('foo', addr_spec='bar@baz')
+        self.assertEqual(a.display_name, 'foo')
+        self.assertEqual(a.username, 'bar')
+        self.assertEqual(a.domain, 'baz')
+        self.assertEqual(a.addr_spec, 'bar@baz')
+        self.assertEqual(str(a), 'foo <bar@baz>')
+
+    def test_address_with_no_display_name(self):
+        a = Address(addr_spec='bar@baz')
+        self.assertEqual(a.display_name, '')
+        self.assertEqual(a.username, 'bar')
+        self.assertEqual(a.domain, 'baz')
+        self.assertEqual(a.addr_spec, 'bar@baz')
+        self.assertEqual(str(a), 'bar@baz')
+
+    def test_null_address(self):
+        a = Address()
+        self.assertEqual(a.display_name, '')
+        self.assertEqual(a.username, '')
+        self.assertEqual(a.domain, '')
+        self.assertEqual(a.addr_spec, '<>')
+        self.assertEqual(str(a), '<>')
+
+    def test_domain_only(self):
+        # This isn't really a valid address.
+        a = Address(domain='buzz')
+        self.assertEqual(a.display_name, '')
+        self.assertEqual(a.username, '')
+        self.assertEqual(a.domain, 'buzz')
+        self.assertEqual(a.addr_spec, '@buzz')
+        self.assertEqual(str(a), '@buzz')
+
+    def test_username_only(self):
+        # This isn't really a valid address.
+        a = Address(username='buzz')
+        self.assertEqual(a.display_name, '')
+        self.assertEqual(a.username, 'buzz')
+        self.assertEqual(a.domain, '')
+        self.assertEqual(a.addr_spec, 'buzz')
+        self.assertEqual(str(a), 'buzz')
+
+    def test_display_name_only(self):
+        a = Address('buzz')
+        self.assertEqual(a.display_name, 'buzz')
+        self.assertEqual(a.username, '')
+        self.assertEqual(a.domain, '')
+        self.assertEqual(a.addr_spec, '<>')
+        self.assertEqual(str(a), 'buzz <>')
+
+    def test_quoting(self):
+        # Ideally we'd check every special individually, but I'm not up for
+        # writing that many tests.
+        a = Address('Sara J.', 'bad name', 'example.com')
+        self.assertEqual(a.display_name, 'Sara J.')
+        self.assertEqual(a.username, 'bad name')
+        self.assertEqual(a.domain, 'example.com')
+        self.assertEqual(a.addr_spec, '"bad name"@example.com')
+        self.assertEqual(str(a), '"Sara J." <"bad name"@example.com>')
+
+    def test_il8n(self):
+        a = Address('Éric', 'wok', 'exàmple.com')
+        self.assertEqual(a.display_name, 'Éric')
+        self.assertEqual(a.username, 'wok')
+        self.assertEqual(a.domain, 'exàmple.com')
+        self.assertEqual(a.addr_spec, 'wok@exàmple.com')
+        self.assertEqual(str(a), 'Éric <wok@exàmple.com>')
+
+    # XXX: there is an API design issue that needs to be solved here.
+    #def test_non_ascii_username_raises(self):
+    #    with self.assertRaises(ValueError):
+    #        Address('foo', 'wők', 'example.com')
+
+    def test_non_ascii_username_in_addr_spec_raises(self):
+        with self.assertRaises(ValueError):
+            Address('foo', addr_spec='wők@example.com')
+
+    def test_address_addr_spec_and_username_raises(self):
+        with self.assertRaises(TypeError):
+            Address('foo', username='bing', addr_spec='bar@baz')
+
+    def test_address_addr_spec_and_domain_raises(self):
+        with self.assertRaises(TypeError):
+            Address('foo', domain='bing', addr_spec='bar@baz')
+
+    def test_address_addr_spec_and_username_and_domain_raises(self):
+        with self.assertRaises(TypeError):
+            Address('foo', username='bong', domain='bing', addr_spec='bar@baz')
+
+    def test_space_in_addr_spec_username_raises(self):
+        with self.assertRaises(ValueError):
+            Address('foo', addr_spec="bad name@example.com")
+
+    def test_bad_addr_sepc_raises(self):
+        with self.assertRaises(ValueError):
+            Address('foo', addr_spec="name@ex[]ample.com")
+
+    def test_empty_group(self):
+        g = Group('foo')
+        self.assertEqual(g.display_name, 'foo')
+        self.assertEqual(g.addresses, tuple())
+        self.assertEqual(str(g), 'foo:;')
+
+    def test_empty_group_list(self):
+        g = Group('foo', addresses=[])
+        self.assertEqual(g.display_name, 'foo')
+        self.assertEqual(g.addresses, tuple())
+        self.assertEqual(str(g), 'foo:;')
+
+    def test_null_group(self):
+        g = Group()
+        self.assertIsNone(g.display_name)
+        self.assertEqual(g.addresses, tuple())
+        self.assertEqual(str(g), 'None:;')
+
+    def test_group_with_addresses(self):
+        addrs = [Address('b', 'b', 'c'), Address('a', 'b','c')]
+        g = Group('foo', addrs)
+        self.assertEqual(g.display_name, 'foo')
+        self.assertEqual(g.addresses, tuple(addrs))
+        self.assertEqual(str(g), 'foo: b <b@c>, a <b@c>;')
+
+    def test_group_with_addresses_no_display_name(self):
+        addrs = [Address('b', 'b', 'c'), Address('a', 'b','c')]
+        g = Group(addresses=addrs)
+        self.assertIsNone(g.display_name)
+        self.assertEqual(g.addresses, tuple(addrs))
+        self.assertEqual(str(g), 'None: b <b@c>, a <b@c>;')
+
+    def test_group_with_one_address_no_display_name(self):
+        addrs = [Address('b', 'b', 'c')]
+        g = Group(addresses=addrs)
+        self.assertIsNone(g.display_name)
+        self.assertEqual(g.addresses, tuple(addrs))
+        self.assertEqual(str(g), 'b <b@c>')
+
+    def test_display_name_quoting(self):
+        g = Group('foo.bar')
+        self.assertEqual(g.display_name, 'foo.bar')
+        self.assertEqual(g.addresses, tuple())
+        self.assertEqual(str(g), '"foo.bar":;')
+
+    def test_display_name_blanks_not_quoted(self):
+        g = Group('foo bar')
+        self.assertEqual(g.display_name, 'foo bar')
+        self.assertEqual(g.addresses, tuple())
+        self.assertEqual(str(g), 'foo bar:;')
+
+
+class TestFolding(TestHeaderBase):
+
+    def test_short_unstructured(self):
+        h = self.make_header('subject', 'this is a test')
+        self.assertEqual(h.fold(policy=self.policy),
+                         'subject: this is a test\n')
+
+    def test_long_unstructured(self):
+        h = self.make_header('Subject', 'This is a long header '
+            'line that will need to be folded into two lines '
+            'and will demonstrate basic folding')
+        self.assertEqual(h.fold(policy=self.policy),
+                        'Subject: This is a long header line that will '
+                            'need to be folded into two lines\n'
+                        ' and will demonstrate basic folding\n')
+
+    def test_unstructured_short_max_line_length(self):
+        h = self.make_header('Subject', 'this is a short header '
+            'that will be folded anyway')
+        self.assertEqual(
+            h.fold(policy=policy.default.clone(max_line_length=20)),
+            textwrap.dedent("""\
+                Subject: this is a
+                 short header that
+                 will be folded
+                 anyway
+                """))
+
+    def test_fold_unstructured_single_word(self):
+        h = self.make_header('Subject', 'test')
+        self.assertEqual(h.fold(policy=self.policy), 'Subject: test\n')
+
+    def test_fold_unstructured_short(self):
+        h = self.make_header('Subject', 'test test test')
+        self.assertEqual(h.fold(policy=self.policy),
+                        'Subject: test test test\n')
+
+    def test_fold_unstructured_with_overlong_word(self):
+        h = self.make_header('Subject', 'thisisaverylonglineconsistingofa'
+            'singlewordthatwontfit')
+        self.assertEqual(
+            h.fold(policy=policy.default.clone(max_line_length=20)),
+            'Subject: thisisaverylonglineconsistingofasinglewordthatwontfit\n')
+
+    def test_fold_unstructured_with_two_overlong_words(self):
+        h = self.make_header('Subject', 'thisisaverylonglineconsistingofa'
+            'singlewordthatwontfit plusanotherverylongwordthatwontfit')
+        self.assertEqual(
+            h.fold(policy=policy.default.clone(max_line_length=20)),
+            'Subject: thisisaverylonglineconsistingofasinglewordthatwontfit\n'
+                ' plusanotherverylongwordthatwontfit\n')
+
+    def test_fold_unstructured_with_slightly_long_word(self):
+        h = self.make_header('Subject', 'thislongwordislessthanmaxlinelen')
+        self.assertEqual(
+            h.fold(policy=policy.default.clone(max_line_length=35)),
+            'Subject:\n thislongwordislessthanmaxlinelen\n')
+
+    def test_fold_unstructured_with_commas(self):
+        # The old wrapper would fold this at the commas.
+        h = self.make_header('Subject', "This header is intended to "
+            "demonstrate, in a fairly susinct way, that we now do "
+            "not give a , special treatment in unstructured headers.")
+        self.assertEqual(
+            h.fold(policy=policy.default.clone(max_line_length=60)),
+            textwrap.dedent("""\
+                Subject: This header is intended to demonstrate, in a fairly
+                 susinct way, that we now do not give a , special treatment
+                 in unstructured headers.
+                 """))
+
+    def test_fold_address_list(self):
+        h = self.make_header('To', '"Theodore H. Perfect" <yes@man.com>, '
+            '"My address is very long because my name is long" <foo@bar.com>, '
+            '"Only A. Friend" <no@yes.com>')
+        self.assertEqual(h.fold(policy=self.policy), textwrap.dedent("""\
+            To: "Theodore H. Perfect" <yes@man.com>,
+             "My address is very long because my name is long" <foo@bar.com>,
+             "Only A. Friend" <no@yes.com>
+             """))
+
+    def test_fold_date_header(self):
+        h = self.make_header('Date', 'Sat, 2 Feb 2002 17:00:06 -0800')
+        self.assertEqual(h.fold(policy=self.policy),
+                        'Date: Sat, 02 Feb 2002 17:00:06 -0800\n')
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/Lib/test/test_email/test_generator.py b/Lib/test/test_email/test_generator.py
index 8f5fde7..c1af024 100644
--- a/Lib/test/test_email/test_generator.py
+++ b/Lib/test/test_email/test_generator.py
@@ -6,14 +6,16 @@ from email.generator import Generator, BytesGenerator
 from email import policy
 from test.test_email import TestEmailBase
 
-# XXX: move generator tests from test_email into here at some point.
 
+class TestGeneratorBase:
 
-class TestGeneratorBase():
+    policy = policy.default
 
-    policy = policy.compat32
+    def msgmaker(self, msg, policy=None):
+        policy = self.policy if policy is None else policy
+        return self.msgfunc(msg, policy=policy)
 
-    long_subject = {
+    refold_long_expected = {
         0: textwrap.dedent("""\
             To: whom_it_may_concern@example.com
             From: nobody_you_want_to_know@example.com
@@ -23,33 +25,32 @@ class TestGeneratorBase():
 
             None
             """),
+        # From is wrapped because wrapped it fits in 40.
         40: textwrap.dedent("""\
             To: whom_it_may_concern@example.com
-            From:\x20
+            From:
              nobody_you_want_to_know@example.com
             Subject: We the willing led by the
-             unknowing are doing the
-             impossible for the ungrateful. We have
-             done so much for so long with so little
-             we are now qualified to do anything
-             with nothing.
+             unknowing are doing the impossible for
+             the ungrateful. We have done so much
+             for so long with so little we are now
+             qualified to do anything with nothing.
 
             None
             """),
+        # Neither to nor from fit even if put on a new line,
+        # so we leave them sticking out on the first line.
         20: textwrap.dedent("""\
-            To:\x20
-             whom_it_may_concern@example.com
-            From:\x20
-             nobody_you_want_to_know@example.com
+            To: whom_it_may_concern@example.com
+            From: nobody_you_want_to_know@example.com
             Subject: We the
              willing led by the
              unknowing are doing
-             the
-             impossible for the
-             ungrateful. We have
-             done so much for so
-             long with so little
-             we are now
+             the impossible for
+             the ungrateful. We
+             have done so much
+             for so long with so
+             little we are now
              qualified to do
              anything with
              nothing.
@@ -57,65 +58,90 @@ class TestGeneratorBase():
             None
             """),
         }
-    long_subject[100] = long_subject[0]
-
-    def maxheaderlen_parameter_test(self, n):
-        msg = self.msgmaker(self.typ(self.long_subject[0]))
+    refold_long_expected[100] = refold_long_expected[0]
+
+    refold_all_expected = refold_long_expected.copy()
+    refold_all_expected[0] = (
+            "To: whom_it_may_concern@example.com\n"
+            "From: nobody_you_want_to_know@example.com\n"
+            "Subject: We the willing led by the unknowing are doing the "
+              "impossible for the ungrateful. We have done so much for "
+              "so long with so little we are now qualified to do anything "
+              "with nothing.\n"
+              "\n"
+              "None\n")
+    refold_all_expected[100] = (
+            "To: whom_it_may_concern@example.com\n"
+            "From: nobody_you_want_to_know@example.com\n"
+            "Subject: We the willing led by the unknowing are doing the "
+                "impossible for the ungrateful. We have\n"
+              " done so much for so long with so little we are now qualified "
+                "to do anything with nothing.\n"
+              "\n"
+              "None\n")
+
+    def _test_maxheaderlen_parameter(self, n):
+        msg = self.msgmaker(self.typ(self.refold_long_expected[0]))
         s = self.ioclass()
-        g = self.genclass(s, maxheaderlen=n)
+        g = self.genclass(s, maxheaderlen=n, policy=self.policy)
         g.flatten(msg)
-        self.assertEqual(s.getvalue(), self.typ(self.long_subject[n]))
+        self.assertEqual(s.getvalue(), self.typ(self.refold_long_expected[n]))
 
-    def test_maxheaderlen_parameter_0(self):
-        self.maxheaderlen_parameter_test(0)
+    for n in refold_long_expected:
+        locals()['test_maxheaderlen_parameter_' + str(n)] = (
+            lambda self, n=n:
+                self._test_maxheaderlen_parameter(n))
 
-    def test_maxheaderlen_parameter_100(self):
-        self.maxheaderlen_parameter_test(100)
-
-    def test_maxheaderlen_parameter_40(self):
-        self.maxheaderlen_parameter_test(40)
-
-    def test_maxheaderlen_parameter_20(self):
-        self.maxheaderlen_parameter_test(20)
-
-    def maxheaderlen_policy_test(self, n):
-        msg = self.msgmaker(self.typ(self.long_subject[0]))
+    def _test_max_line_length_policy(self, n):
+        msg = self.msgmaker(self.typ(self.refold_long_expected[0]))
         s = self.ioclass()
-        g = self.genclass(s, policy=policy.default.clone(max_line_length=n))
+        g = self.genclass(s, policy=self.policy.clone(max_line_length=n))
         g.flatten(msg)
-        self.assertEqual(s.getvalue(), self.typ(self.long_subject[n]))
-
-    def test_maxheaderlen_policy_0(self):
-        self.maxheaderlen_policy_test(0)
-
-    def test_maxheaderlen_policy_100(self):
-        self.maxheaderlen_policy_test(100)
-
-    def test_maxheaderlen_policy_40(self):
-        self.maxheaderlen_policy_test(40)
+        self.assertEqual(s.getvalue(), self.typ(self.refold_long_expected[n]))
 
-    def test_maxheaderlen_policy_20(self):
-        self.maxheaderlen_policy_test(20)
+    for n in refold_long_expected:
+        locals()['test_max_line_length_policy' + str(n)] = (
+            lambda self, n=n:
+                self._test_max_line_length_policy(n))
 
-    def maxheaderlen_parm_overrides_policy_test(self, n):
-        msg = self.msgmaker(self.typ(self.long_subject[0]))
+    def _test_maxheaderlen_parm_overrides_policy(self, n):
+        msg = self.msgmaker(self.typ(self.refold_long_expected[0]))
         s = self.ioclass()
         g = self.genclass(s, maxheaderlen=n,
-                          policy=policy.default.clone(max_line_length=10))
+                          policy=self.policy.clone(max_line_length=10))
         g.flatten(msg)
-        self.assertEqual(s.getvalue(), self.typ(self.long_subject[n]))
+        self.assertEqual(s.getvalue(), self.typ(self.refold_long_expected[n]))
 
-    def test_maxheaderlen_parm_overrides_policy_0(self):
-        self.maxheaderlen_parm_overrides_policy_test(0)
+    for n in refold_long_expected:
+        locals()['test_maxheaderlen_parm_overrides_policy' + str(n)] = (
+            lambda self, n=n:
+                self._test_maxheaderlen_parm_overrides_policy(n))
 
-    def test_maxheaderlen_parm_overrides_policy_100(self):
-        self.maxheaderlen_parm_overrides_policy_test(100)
+    def _test_refold_none_does_not_fold(self, n):
+        msg = self.msgmaker(self.typ(self.refold_long_expected[0]))
+        s = self.ioclass()
+        g = self.genclass(s, policy=self.policy.clone(refold_source='none',
+                                                      max_line_length=n))
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), self.typ(self.refold_long_expected[0]))
+
+    for n in refold_long_expected:
+        locals()['test_refold_none_does_not_fold' + str(n)] = (
+            lambda self, n=n:
+                self._test_refold_none_does_not_fold(n))
 
-    def test_maxheaderlen_parm_overrides_policy_40(self):
-        self.maxheaderlen_parm_overrides_policy_test(40)
+    def _test_refold_all(self, n):
+        msg = self.msgmaker(self.typ(self.refold_long_expected[0]))
+        s = self.ioclass()
+        g = self.genclass(s, policy=self.policy.clone(refold_source='all',
+                                                      max_line_length=n))
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), self.typ(self.refold_all_expected[n]))
 
-    def test_maxheaderlen_parm_overrides_policy_20(self):
-        self.maxheaderlen_parm_overrides_policy_test(20)
+    for n in refold_long_expected:
+        locals()['test_refold_all' + str(n)] = (
+            lambda self, n=n:
+                self._test_refold_all(n))
 
     def test_crlf_control_via_policy(self):
         source = "Subject: test\r\n\r\ntest body\r\n"
@@ -138,30 +164,24 @@ class TestGeneratorBase():
 
 class TestGenerator(TestGeneratorBase, TestEmailBase):
 
+    msgfunc = staticmethod(message_from_string)
     genclass = Generator
     ioclass = io.StringIO
     typ = str
 
-    def msgmaker(self, msg, policy=None):
-        policy = self.policy if policy is None else policy
-        return message_from_string(msg, policy=policy)
-
 
 class TestBytesGenerator(TestGeneratorBase, TestEmailBase):
 
+    msgfunc = staticmethod(message_from_bytes)
     genclass = BytesGenerator
     ioclass = io.BytesIO
     typ = lambda self, x: x.encode('ascii')
 
-    def msgmaker(self, msg, policy=None):
-        policy = self.policy if policy is None else policy
-        return message_from_bytes(msg, policy=policy)
-
     def test_cte_type_7bit_handles_unknown_8bit(self):
         source = ("Subject: Maintenant je vous présente mon "
                  "collègue\n\n").encode('utf-8')
-        expected = ('Subject: =?unknown-8bit?q?Maintenant_je_vous_pr=C3=A9sente_mon_'
-                    'coll=C3=A8gue?=\n\n').encode('ascii')
+        expected = ('Subject: Maintenant je vous =?unknown-8bit?q?'
+                    'pr=C3=A9sente_mon_coll=C3=A8gue?=\n\n').encode('ascii')
         msg = message_from_bytes(source)
         s = io.BytesIO()
         g = BytesGenerator(s, policy=self.policy.clone(cte_type='7bit'))
diff --git a/Lib/test/test_email/test_pickleable.py b/Lib/test/test_email/test_pickleable.py
new file mode 100644
index 0000000..e4c77ca
--- /dev/null
+++ b/Lib/test/test_email/test_pickleable.py
@@ -0,0 +1,57 @@
+import unittest
+import textwrap
+import copy
+import pickle
+from email import policy
+from email import message_from_string
+from email._headerregistry import HeaderRegistry
+from test.test_email import TestEmailBase
+
+class TestPickleCopyHeader(TestEmailBase):
+
+    unstructured = HeaderRegistry()('subject', 'this is a test')
+
+    def test_deepcopy_unstructured(self):
+        h = copy.deepcopy(self.unstructured)
+        self.assertEqual(str(h), str(self.unstructured))
+
+    def test_pickle_unstructured(self):
+        p = pickle.dumps(self.unstructured)
+        h = pickle.loads(p)
+        self.assertEqual(str(h), str(self.unstructured))
+
+    address = HeaderRegistry()('from', 'frodo@mordor.net')
+
+    def test_deepcopy_address(self):
+        h = copy.deepcopy(self.address)
+        self.assertEqual(str(h), str(self.address))
+
+    def test_pickle_address(self):
+        p = pickle.dumps(self.address)
+        h = pickle.loads(p)
+        self.assertEqual(str(h), str(self.address))
+
+
+class TestPickleCopyMessage(TestEmailBase):
+
+    testmsg = message_from_string(textwrap.dedent("""\
+            From: frodo@mordor.net
+            To: bilbo@underhill.org
+            Subject: help
+
+            I think I forgot the ring.
+            """), policy=policy.default)
+
+    def test_deepcopy(self):
+        msg2 = copy.deepcopy(self.testmsg)
+        self.assertEqual(msg2.as_string(), self.testmsg.as_string())
+
+    def test_pickle(self):
+        p = pickle.dumps(self.testmsg)
+        msg2 = pickle.loads(p)
+        self.assertEqual(msg2.as_string(), self.testmsg.as_string())
+
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/Lib/test/test_email/test_policy.py b/Lib/test/test_email/test_policy.py
index 07925a7..45a7666 100644
--- a/Lib/test/test_email/test_policy.py
+++ b/Lib/test/test_email/test_policy.py
@@ -5,49 +5,70 @@ import unittest
 import email.policy
 import email.parser
 import email.generator
+from email import _headerregistry
+
+def make_defaults(base_defaults, differences):
+    defaults = base_defaults.copy()
+    defaults.update(differences)
+    return defaults
 
 class PolicyAPITests(unittest.TestCase):
 
     longMessage = True
 
-    # These default values are the ones set on email.policy.default.
-    # If any of these defaults change, the docs must be updated.
-    policy_defaults = {
+    # Base default values.
+    compat32_defaults = {
         'max_line_length':          78,
         'linesep':                  '\n',
         'cte_type':                 '8bit',
         'raise_on_defect':          False,
         }
-
-    # For each policy under test, we give here the values of the attributes
-    # that are different from the defaults for that policy.
+    # These default values are the ones set on email.policy.default.
+    # If any of these defaults change, the docs must be updated.
+    policy_defaults = compat32_defaults.copy()
+    policy_defaults.update({
+        'raise_on_defect':          False,
+        'header_factory':           email.policy.EmailPolicy.header_factory,
+        'refold_source':            'long',
+        })
+
+    # For each policy under test, we give here what we expect the defaults to
+    # be for that policy.  The second argument to make defaults is the
+    # difference between the base defaults and that for the particular policy.
+    new_policy = email.policy.EmailPolicy()
     policies = {
-        email.policy.Compat32(): {},
-        email.policy.compat32: {},
-        email.policy.default: {},
-        email.policy.SMTP: {'linesep': '\r\n'},
-        email.policy.HTTP: {'linesep': '\r\n', 'max_line_length': None},
-        email.policy.strict: {'raise_on_defect': True},
+        email.policy.compat32: make_defaults(compat32_defaults, {}),
+        email.policy.default: make_defaults(policy_defaults, {}),
+        email.policy.SMTP: make_defaults(policy_defaults,
+                                         {'linesep': '\r\n'}),
+        email.policy.HTTP: make_defaults(policy_defaults,
+                                         {'linesep': '\r\n',
+                                          'max_line_length': None}),
+        email.policy.strict: make_defaults(policy_defaults,
+                                           {'raise_on_defect': True}),
+        new_policy: make_defaults(policy_defaults, {}),
         }
+    # Creating a new policy creates a new header factory.  There is a test
+    # later that proves this.
+    policies[new_policy]['header_factory'] = new_policy.header_factory
 
     def test_defaults(self):
-        for policy, changed_defaults in self.policies.items():
-            expected = self.policy_defaults.copy()
-            expected.update(changed_defaults)
+        for policy, expected in self.policies.items():
             for attr, value in expected.items():
                 self.assertEqual(getattr(policy, attr), value,
                                 ("change {} docs/docstrings if defaults have "
                                 "changed").format(policy))
 
     def test_all_attributes_covered(self):
-        for attr in dir(email.policy.default):
-            if (attr.startswith('_') or
-               isinstance(getattr(email.policy.Policy, attr),
-                          types.FunctionType)):
-                continue
-            else:
-                self.assertIn(attr, self.policy_defaults,
-                              "{} is not fully tested".format(attr))
+        for policy, expected in self.policies.items():
+            for attr in dir(policy):
+                if (attr.startswith('_') or
+                        isinstance(getattr(email.policy.EmailPolicy, attr),
+                              types.FunctionType)):
+                    continue
+                else:
+                    self.assertIn(attr, expected,
+                                  "{} is not fully tested".format(attr))
 
     def test_abc(self):
         with self.assertRaises(TypeError) as cm:
@@ -62,18 +83,20 @@ class PolicyAPITests(unittest.TestCase):
             self.assertIn(method, msg)
 
     def test_policy_is_immutable(self):
-        for policy in self.policies:
-            for attr in self.policy_defaults:
+        for policy, defaults in self.policies.items():
+            for attr in defaults:
                 with self.assertRaisesRegex(AttributeError, attr+".*read-only"):
                     setattr(policy, attr, None)
             with self.assertRaisesRegex(AttributeError, 'no attribute.*foo'):
                 policy.foo = None
 
-    def test_set_policy_attrs_when_calledl(self):
-        testattrdict = { attr: None for attr in self.policy_defaults }
-        for policyclass in self.policies:
+    def test_set_policy_attrs_when_cloned(self):
+        # None of the attributes has a default value of None, so we set them
+        # all to None in the clone call and check that it worked.
+        for policyclass, defaults in self.policies.items():
+            testattrdict = {attr: None for attr in defaults}
             policy = policyclass.clone(**testattrdict)
-            for attr in self.policy_defaults:
+            for attr in defaults:
                 self.assertIsNone(getattr(policy, attr))
 
     def test_reject_non_policy_keyword_when_called(self):
@@ -105,7 +128,7 @@ class PolicyAPITests(unittest.TestCase):
                 self.defects = []
         obj = Dummy()
         defect = object()
-        policy = email.policy.Compat32()
+        policy = email.policy.EmailPolicy()
         policy.register_defect(obj, defect)
         self.assertEqual(obj.defects, [defect])
         defect2 = object()
@@ -134,7 +157,7 @@ class PolicyAPITests(unittest.TestCase):
         email.policy.default.handle_defect(foo, defect2)
         self.assertEqual(foo.defects, [defect1, defect2])
 
-    class MyPolicy(email.policy.Compat32):
+    class MyPolicy(email.policy.EmailPolicy):
         defects = None
         def __init__(self, *args, **kw):
             super().__init__(*args, defects=[], **kw)
@@ -159,6 +182,49 @@ class PolicyAPITests(unittest.TestCase):
         self.assertEqual(my_policy.defects, [defect1, defect2])
         self.assertEqual(foo.defects, [])
 
+    def test_default_header_factory(self):
+        h = email.policy.default.header_factory('Test', 'test')
+        self.assertEqual(h.name, 'Test')
+        self.assertIsInstance(h, _headerregistry.UnstructuredHeader)
+        self.assertIsInstance(h, _headerregistry.BaseHeader)
+
+    class Foo:
+        parse = _headerregistry.UnstructuredHeader.parse
+
+    def test_each_Policy_gets_unique_factory(self):
+        policy1 = email.policy.EmailPolicy()
+        policy2 = email.policy.EmailPolicy()
+        policy1.header_factory.map_to_type('foo', self.Foo)
+        h = policy1.header_factory('foo', 'test')
+        self.assertIsInstance(h, self.Foo)
+        self.assertNotIsInstance(h, _headerregistry.UnstructuredHeader)
+        h = policy2.header_factory('foo', 'test')
+        self.assertNotIsInstance(h, self.Foo)
+        self.assertIsInstance(h, _headerregistry.UnstructuredHeader)
+
+    def test_clone_copies_factory(self):
+        policy1 = email.policy.EmailPolicy()
+        policy2 = policy1.clone()
+        policy1.header_factory.map_to_type('foo', self.Foo)
+        h = policy1.header_factory('foo', 'test')
+        self.assertIsInstance(h, self.Foo)
+        h = policy2.header_factory('foo', 'test')
+        self.assertIsInstance(h, self.Foo)
+
+    def test_new_factory_overrides_default(self):
+        mypolicy = email.policy.EmailPolicy()
+        myfactory = mypolicy.header_factory
+        newpolicy = mypolicy + email.policy.strict
+        self.assertEqual(newpolicy.header_factory, myfactory)
+        newpolicy = email.policy.strict + mypolicy
+        self.assertEqual(newpolicy.header_factory, myfactory)
+
+    def test_adding_default_policies_preserves_default_factory(self):
+        newpolicy = email.policy.default + email.policy.strict
+        self.assertEqual(newpolicy.header_factory,
+                         email.policy.EmailPolicy.header_factory)
+        self.assertEqual(newpolicy.__dict__, {'raise_on_defect': True})
+
     # XXX: Need subclassing tests.
     # For adding subclassed objects, make sure the usual rules apply (subclass
     # wins), but that the order still works (right overrides left).