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<html>
<!--
Specifications for the Tk HTML Widget
$Revision$
Copyright (C) 1997, 1998, 1999 D. Richard Hipp
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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This program is distributed in the hope that it will be useful,
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Author Contact Information:
drh@acm.org
http://www.hwaci.com/drh/
@(#) $Id$
-->
<head>
<title>Interface Specification For The HTML Widget</title>
</head>
<body bgcolor=white>
<h1>Interface Specification For The HTML Widget</h1>
<p>This is a draft interface specification for the Tk HTML
widget currently under development.
Since it is still a draft, it is subject to change.
Eventually, the interface will stabilize and this interface
specification will morph into a manual page.</p>
<h2>Configuration Options</h2>
<table cellspacing=10>
<tr><td valign=top><tt>-appletcommand</tt></td>
<td>
<p>This option specifies the name of the Tcl procedure to invoke when the
<tt><applet>...</applet></tt> tag sequence is seen. The html
widget will append two arguments to the procedure before calling it.
The first argument is the name of a widget that the callback should
create to hold the applet.
The second argument is
a list of name/value pairs which are the arguments to
the <tt><applet></tt> tag.</p>
<p>The text between <tt><applet></tt> and <tt></applet></tt>
is normally suppressed.
However, if the <tt>-appletcommand</tt> option is set to the empty string,
the <tt><applet></tt> tag is ignored and all text between
<tt><applet></tt> and <tt></applet></tt> is displayed
normally.</p>
<p>"<embed>" is treated as an alias for
"<applet></applet>".</p>
</td></tr>
<tr><td valign=top><tt>-background</tt></td>
<td>
<p>The background color for the widget.</p>
<p>Note that the <tt><body bgcolor=...></tt> HTML tag does not
automatically cause the widget to change its background color. If
you want the background color to change in response to this HTML tag,
then your Tcl script should intercept
the <tt><body></tt> tag using the
``<tt>token handler</tt>'' widget command (described below) and
change the background color manually.</p>
</td></tr>
<tr><td valign=top><tt>-base</tt></td>
<td>
<p>The base URI for the current document. This should be set to
the URI that was used to retrieve the document before parsing
begins.</p>
</td></tr>
<tr><td valign=top><tt>-bd</tt><td>An alias for <tt>-borderwidth</tt>
<tr><td valign=top><tt>-bg</tt><td>An alias for <tt>-background</tt>
<tr><td valign=top><tt>-borderwidth</tt></td>
<td>
<p>The width of the 3-D border drawn around the parameter of the widget, in
pixels.</p>
</td></tr>
<tr><td valign=top><tt>-cursor</tt></td>
<td>
<p>The cursor displayed when the pointer is positioned over the HTML widget.
If {}, the cursor reverts to its default shape.</p>
</td></tr>
<tr><td valign=top><tt>-exportselection</tt></td>
</tr>
<tr><td valign=top><tt>-fontcommand</tt></td>
<td>
<p>The name of a TCL procedure that is used to convert HTML font names
into TCL font names. A default built-in procedure is used if the value
of this option is {}.</p>
<p>When the HTML widget needs a new font, it calls this procedure with
two arguments. This first argument is the font size expressed as an
integer between 1 and 7. The standard size is 4. The second argument
is a set of between 0 and 3 keywords drawn from the following set:
"bold", "italic", and "fixed". If the "bold" keyword is present in
the second argument, the font returned should be bold. If the "italic"
keyword is present, the font should be italic. If the "fixed" keyword
is present, the font should be fixed-width. The TCL procedure should
return the name of the TCL font that the HTML widget will use to render
the given HTML font. If the TCL procedure returns an empty string,
then the built-in default procedure is used to determine the font.</p>
<p>Examples: This is {4 {}}. <tt>This is {4 fixed}</tt>.
<small>This is {3 {}}</small>. <large><tt><bold>This is {5 {fixed bold}}
</bold></tt></large></p>
</td></tr>
<tr><td valign=top><tt>-fg</tt></td>
<td>An alias for <tt>-foreground</tt>.</td>
</tr>
<tr><td valign=top><tt>-foreground</tt></td>
<td>
The default foreground color in which HTML text is rendered.
The HTML can override this using the <tt>color=...</tt> attribute
on various HTML tags.
</td></tr>
<tr><td valign=top>
<code>-formcommand <var>string</var></code>
</td><td>
Declares a handler for everything to do with forms within a document.
Arguments will be appended to <var>string</var> and the result evaluated
during parsing (for form creation) and when the widget is cleared (for
form cleanup). The first argument is a token for
identifying a form. The second argument selects the action to perform.
The remaining arguments depend on the action, as follows.
<dl><dt><code><var>string token</var> form <var>URL method attrs</var></code>
<dd>The handler should begin taking notes for form <var>token</var>,
especially the (resolved) <var>URL</var> of the action and the
<var>method</var> to be applied. The raw attributes of the FORM element
are in the pairlist <var>attrs</var>.
<dt><code><var>string token</var> flush</code>
<dd>When the document is cleared, the widget will destroy all the windows
it requested. This handler should clean up anything else
it created for that form.
<dt><code><var>string token</var> input <var>path attrs</var></code>
<dd>The handler should create a window named <var>path</var>
appropriate for the element described by the <var>attrs</var>.
The widget will map the window into its rendering appropriately.
<p>It is not an error for the handler to return without creating such a window
(it's natural in the case of type=hidden); the widget simply
ignores the element in that case.
The attributes are the raw values in the HTML, with one exception;
a <code>src</code> will be resolved before the handler is called.
<dt><code><var>string token</var> textarea <var>path attrs initial</var></code>
<dd>The handler should create a window (a single Text, or a Frame with Text
and Scrollbars, or whatever) appropriate for a <textarea> and
initialise it to the <var>initial</var> string.
<dt><code><var>string token</var> select <var>path attrs choices initial</var></code>
<dd><em><select> is quite a complicated case...</em>
The handler should create a window
appropriate for a <select> of the given attributes and
present the list of <var>choices</var>. Each choice is a pair, the
value and its label. <var>initial</var> is a list of values initially
selected. <em>This approach is somewhat questionable but should do
most of the time.</em>
</dl>
Caution: Be very careful to avoid confusing HTML variables with TCL
variables. It may be tempting to use the <code>name</code> attribute
fairly directly to link
together related widgets, but it will likely cause incorrect
behaviours. Also be careful to observe the order in which the elements are
created; this determines the order in which they must be submitted.
A default form handler with the correct bahaviour written in TCL will be
bundled with the widget.
<p>The attribute names will be downcased within <var>attrs</var>.
</td></tr>
<tr><td valign=top><tt>-framecommand</tt><td>
The script specified by this option is invoked when the HTML parser
encounters a <tt><frameset>...</frameset></tt> tag sequence.
The arguments to the script are TBD.
If the value of the option is the empty string, then the text within
the <tt><noframe>...</noframe></tt> tag sequence is displayed.
<tr><td valign=top><tt>-height</tt><td>
Specifies the height of the area into which HTML is rendered.
This value plus twice the <tt>-padx</tt>, <tt>-borderwidth</tt> and
<tt>-highlightthickness</tt> values is the total height of the widget.
<tr><td valign=top><tt>-highlightbackground</tt><td>
<tr><td valign=top><tt>-highlightcolor</tt><td>
<tr><td valign=top><tt>-highlightthickness</tt><td>
<tr><td valign=top><tt>-hyperlinkcommand</tt></td>
<td>
The script specified by this option is invoked whenever the user
clicks on a hyperlink on the HTML page. Before invoking this
script, the URI for the hyperlink is appended.
</td></tr>
<tr><td valign=top><tt>-imagecommand</tt></td>
<td>
When a ``<tt><img src=...></tt>'' tag is encountered, the
HTML widget invokes the script specified by this option in order to
get the name of a Tk image object to display the HTML image.
Before invoking the script, the following arguments are appended:
<ol>
<li>The value of the <tt>src=...</tt> parameter after have been
processed by the resolver.
<li>The value of the <tt>width=...</tt> parameter.
<li>The value of the <tt>height=...</tt> parameter.
<li>A list containing the names and values of all parameters.
</ol>
If the name returned by this script is the empty string, or if the
script is an empty string, then the HTML widget displays the
<tt>alt=...</tt> text of the <tt><img></tt> tag instead of
an image.
</td></tr>
<tr><td valign=top><tt>-isvisitedcommand</tt><td>
When the HTML widget encounters a hyperlink
(``<tt><a href=...></tt>'') it invokes the script specified
by this option in order to determine whether or not the hyperlink
has been visited.
This information is needed to determine what color to use to display
the hyperlink.
<tr><td valign=top><tt>-padx</tt><td>
The amount of extra space to insert between the 3-D border and the
left and right sides of the document text.
<tr><td valign=top><tt>-pady</tt><td>
The amount of extra space to insert between the 3-D border and the top
and bottom of the document text.
<tr><td valign=top><tt>-relief</tt><td>
The relief used to draw the 3-D border.
<tr><td valign=top><tt>-resolvercommand</tt></td>
<td>
<p>The name of a TCL command used to resolve URIs. If blank, a built-in
resolver is used. If a TCL command is specified but it returns
an empty string, the built-in resolver is used then too.
The build-in resolver is based on the algorithm
in section 5.2 of RFC 2396. </p>
<p>Multiple URIs are appended to the TCL command before it is executed.
The first URI is the BASE URI of the document (the URL that specified
by the -base configuration option and updated according to any prior
<BASE> markup). Zero or more additional URIs are
appended to this base. The result of the script should be the resolution
of the whole series or URIs.</p>
</td></tr>
<tr><td valign=top><tt>-rulerelief</tt></td>
<td>
<p>Determines the appearance of the Horizontal Rule (<HR>) markup.
The default is "sunken". This can also be "raised" or "flat". If
"flat", then the <HR> is drawn using a solid line in the current
foreground color. "groove" and "ridge" are the same as "flat".</p>
</td></tr>
<tr><td valign=top><tt>-scriptcommand</tt></td>
<td>
<p>Whenever <SCRIPT>...</SCRIPT> markup is encountered in
the input HTML, the attributes of the <SCRIPT> markup and
the body of the script are appended to this string and the result
is executed as a TCL command. If this options is the empty string,
then the script is ignored.
</td></tr>
<tr><td valign=top><tt>-selectioncolor</tt><td>
The background color used when drawing the selection. The
foreground color for the selection is the same as the regular
foreground color.
<tr><td valign=top><tt>-tablerelief</tt></td>
<td>
<p>Determines the appearance of the borders around tables.
The default is "raised". This can also be "sunken" or "flat". If
"flat", then the borders is drawn using solid lines in the current
foreground color. "groove" and "ridge" are the same as "flat".</p>
</td></tr>
<tr><td valign=top><tt>-takefocus</tt><td>
<tr><td valign=top><tt>-unvisitedcolor</tt><td>
The foreground color used to draw hyperlinks that have not been visited.
<tr><td valign=top><tt>-underlinehyperlinks</tt><td>
Set to TRUE to cause hyperlinks to be drawn using an underlined font.
<tr><td valign=top><tt>-visitedcolor</tt><td>
The foreground color used to draw hyperlinks that have been visited.
<tr><td valign=top><tt>-width</tt><td>
The width of the document text.
This value does not include space allocated for
<tt>-highlightthickness</tt>, <tt>-borderwiddth</tt> or
<tt>-padx</tt>.
<tr><td valign=top><tt>-xscrollcommand</tt><td>
<tr><td valign=top><tt>-yscrollcommand</tt><td>
</table>
<h2>Indices</h2>
Internally, the HTML widget stores the HTML document as a list of
tokens.
Each token is either
<ul>
<li>a contiguous sequence of non-space characters (Text),
<li>a contiguous sequence of spaces, tabs or newlines (Space),
<li>or an HTML markup tag (such as ``<tt><em></tt>''.)
</ul>
Tokens are identified by number.
The first token is ``1'', the second is ``2'' and so forth.
So in its simplest form, an index is just an integer greater than 0.
<p>
Within a single Text or Space token, individual characters are
also identified by number, though the counting starts with 0 instead
of 1.
The character number is connected to the token number by a period.
So, for example, the 4th character in the 9th token would be
``9.3''.
<p>
Two integers separated by a dot is called the <em>connonical</em> form
of an index.
Other index forms are available, including:
<table cellspacing=10>
<tr><td valign=top>end<td>
The keyword ``end'' means one character past
the last character of the last token.
<tr><td valign=top>@X,Y<td>
The character located at screen coordinates X,Y.
<tr><td valign=top>*.last<td>
The second integer can be replaced by the keyword ``last'' to mean the
last character in the token.
<tr><td valign=top>sel.first<td>
This is the first character that is part of the selection.
<tr><td valign=top>sel.last<td>
This is the last character that is part of the selection.
<tr><td valign=top>ins<td>
The character immediately following the insertion cursor.
</table>
<h2>Commands</h2>
<dl>
<dt><b>html</b> <i>window</i> ?<i>options ...</i>?</dt><p>
<dd>
Create a new HTML widget instance named <i>windows</i>
</dd>
<p>
<dt><b>html</b> <b>reformat</b> <i>from to text</i><p>
<dd>
Convert text from one encoding to another. The text is given
in the <i>text</i> argument. The current encoding of the text
is specified by the <i>from</i> argument. This command returns
the same text in the <i>to</i> encoding.
<p>
<i>From</i> and <i>to</i> may be any of the following values:
<p>
<table cellspacing=10>
<tr><td valign=top>plain</td>
<td>
Ordinary text with no characters escaped.
</td></tr>
<tr><td valign=top>http</td>
<td>
The text is encoded in a form suitable for use with the HTTP
protocol. Spaces are converted to "+". Special characters
and escaped as "%aa" where "a" is a hexadecimal digit. A special
character is anything other than an alphanumeric or one of these:
".", "$", "-", or "_".
</td></tr>
<tr><td valign=top>url</td>
<td>
The text is encoded in a form suitable for use as a URI.
Spaces are converted to "+". Special characters
and escaped as "%aa" where "a" is a hexadecimal digit. A special
character is anything other than an alphanumeric or one of these:
".", "$", "-", "_", or "/".
</td></tr>
<tr><td valign=top>html</td>
<td>
The text is encoded in a form suitable for use within HTML.
"&" is encoded as "&amp;", "<" is encoded as "&lt;" and so
forth.
</td></tr>
</table>
<p>
This command is intended to be useful to the TCL procedures that implement
callbacks for the HTML widget.
</dd>
<p>
<dt><b>html</b> <b>uri join</b> <i>scheme authority path query fragment</i><p>
<dd>
This command takes the five main components of a URI and joins them together
into a complete URI. Special characters in any component are escaped.
</dd>
<p>
<dt><b>html</b> <b>uri split</b> <i>uri</i><p>
<dd>
This command takes a single URI and splits it into its five major
components: scheme, authorithy, path, query and fragement. The command
returns a list where each component is an element of the list.
Components missing from the URI are represented as empty elements in
the list.
</dd>
</dl>
<h2>Widget Commands</h2>
<dl>
<dt><i>WIDGET</i>  <tt>cget</tt> <i>config-option</i><p>
<dd>
Return the value of a configuration option. Works just like any
other Tk widget.
<p>
<dt><i>WIDGET</i>  <tt>clear</tt><p>
<dd>
Remove all tokens and text from the HTML widget.
The parser is reset to its initial state.
This routine should be called to changes pages.
<p>
<dt><i>WIDGET</i>  <tt>configure</tt> ?<i>args...</i>?<p>
<dd>
The standard Tk configuration command.
<p>
<dt><i>WIDGET</i>  <tt>href</tt>  <i>X  Y</i><p>
<dd>If the coordinates <i>X Y</i> define a point above a hyperlink,
then this command will return the target URL for that hyperlink.
The URL will be resolved using the -resolvercommand before it
is returned.
<p>
<dt><i>WIDGET</i>  <tt>index</tt>  <i>INDEX  ?COUNT  UNITS?</i></p>
<dd>
Translates <i>INDEX</i> into its connonical form.
The connonical form of an index is two integers separated by a period.
<p>
The optional 3rd and 4th arguments specify a displacement from <i>INDEX</i>
to the value of the index returned.
<i>COUNT</i> can be any integer value, including a negative number.
<i>UNITS</i> must be either ``<tt>char</tt>'' or ``<tt>line</tt>''.
<p>
<dt><i>WIDGET</i>  <tt>insert</tt>  <i>INDEX</i><p>
<dd>
Causes the insertion cursor (a flashing vertical bar) to be positioned
immediately before the character specified by <i>INDEX</i>.
<p>
<dt><i>WIDGET</i>  <tt>names</tt><p>
<dd>
This command causes the widget to scan the entire text of the document
looking for tags of the form ``<tt><a name=...></tt>''.
It returns a list of values of the <tt>name=...</tt> fields.
<p>
The vertical position of the document can be moved to any of these names
using the ``<i>WIDGET</i> <tt>yview</tt> <i>NAME</i>'' command described
below.
<p>
<dt><i>WIDGET</i>  <tt>parse</tt>  <i>HTML-TEXT</i><p>
<dd>Adds the given HTML text to the end of any text previously received
through the <tt>parse</tt> command and parses as much of the text as
possible into tokens.
Afterwards, the display is updated to show the new tokens, if they are
visible.<p>
<dt><i>WIDGET</i> <tt>resolver</tt> ?<i>uri ...</i>?<p>
<dd>The resolver specified by the -resolvercommand option
is called with the
base URI of the document followed
by the remaining arguments to this commant. The result of this
command is the result of the -resolvercommand script.<p>
<dt><i>WIDGET</i>  <tt>selection</tt>  <i>subcommand args...</i><p>
<dd>The selection widget command is used to control the selection.<p>
<dl>
<dt><i>WIDGET</i>  <tt>selection clear</tt><p>
<dd>Clear the current selection. No text will be selected after this
command executes.<p>
<dt><i>WIDGET</i>  <tt>selection set</tt>  <i>START  END</i><p>
<dd>Change the selection to be all text contained within the given
indices.<p>
</dl>
<p>
<dt><i>WIDGET</i>  <tt>text</tt>  <i>subcommand args...</i><p>
<dd>There are several token commands. They all have the common
property that they directly manipulate the text that is displayed.
These commands (none of which are currently implemented) can be used
to build an WYSIWYG editor for HTML.<p>
<dl>
<dt><i>WIDGET</i> <tt>text ascii</tt>  <i>INDEX-1  INDEX-2</i><p>
<dd><p>
Returns plain ASCII text that represents all characters between
<i>INDEX-1</i> and <i>INDEX-2</i>. Formatting tags are omitted.
The <i>INDEX-1</i> character is included by <i>INDEX-2</i> is omitted.
<p>
<dt><i>WIDGET</i> <tt>text delete</tt>  <i>INDEX-1  INDEX-2</i><p>
<dd><p>
All text from <i>INDEX-1</i> up to, but not including <i>INDEX-2</i> is
removed and the display is updated accordingly.
<p>
<dt><i>WIDGET</i> <tt>text html</tt>  <i>INDEX-1  INDEX-2</i><p>
<dd><p>
Returns HTML text that represents all characters and formatting tags
between <i>INDEX-1</i> and <i>INDEX-2</i>.
The <i>INDEX-1</i> character is included by <i>INDEX-2</i> is omitted.
<p>
<dt><i>WIDGET</i> <tt>text insert</tt>  <i>INDEX  TEXT</i><p>
<dd><p>
Inserts one or more characters immediately before the character whose
index is given.
<p>
</dl>
<dt><i>WIDGET</i>  <tt>token</tt>  <i>subcommand args...</i><p>
<dd>There are several token commands. They all have the common
property that they involve the list of tokens into which the
HTML is parsed.<p>
Some of the following subcommands make use of indices. The
character number of these indices is ignored since these commands
deal only with whole tokens.
<p>
<dl>
<dt><i>WIDGET</i> <tt>token append</tt>
<i>TAG ARGUMENTS</i><p>
<dd>
The command causes a token to be appended to the current list of
tokens in the HTML widget. This command is typically used within
a token handler.
<p>
<dt><i>WIDGET</i> <tt>token delete</tt>
<i>INDEX  ?INDEX-2?</i><p>
<dd>
Deletes the single token indentified by the index. If a second index is
given, the range of tokens from the first to the second index inclusive
is deleted.
<p>
<dt><i>WIDGET</i> <tt>token find</tt>
<i>TAG</i><p>
<dd>
Locates all tokens with the given <i>TAG</i> and returns them all
as a list.
Each element of the returned list is a sublist containing the index
for the token and the arguments for the token.
<p>
<dt><i>WIDGET</i> <tt>token get</tt>
<i>INDEX  ?INDEX-2?</i><p>
<dd>
Returns a list of tokens in the range of <i>INDEX</i> through
<i>INDEX-2</i>.
Each element of the list consists of the token tag followed by
the token arguments.
<p>
<dt><i>WIDGET</i> <tt>token handler</tt>
<i>TAG ?SCRIPT?</i><p>
<dd>
This command allows special processing to occur for selected tokens
in the HTML input stream.
The <i>TAG</i> argument is either ``Text'' or ``Space'' or the name
of an HTML tag (ex: ``H3'' or ``/A'').
If a non-empty script is specified for a particular tag, then when
instances of that tag are encountered by the parser, the parser calls the
corresponding script instead of appending the token to the end of the
token list. Before calling the script, three arguments are appended:
<ol>
<li>The token number.
<li>The tag. (ex: <tt>H3</tt>)
<li>A list of name/value pairs describing all arguments to the tag.
</ol>
An empty handler script causes the default processing to occur for
the tag. If the script argument is omitted all together, then
the current value of the token handler for the given tag is returned.
<p>
Only one handler may be defined for each token type. If a new
handler is specified for a token type that previously had a different
handler defined, then the old handler is overwritten by the new.
<p>
<dt><i>WIDGET</i> <tt>token insert</tt>
<i>INDEX  TAG  ARGUMENTS</i><p>
<dd>
Inserts a single token given by <i>TAG</i> and <i>ARGUMENTS</i> into
the token list immediately before <i>INDEX</i>.
<p>
</dl>
<p>
<dt><i>WIDGET</i> <tt>xview</tt> <i>args...</i><p>
<dd>Used to control horizontal scrolling.<p>
<dl>
<dt><i>WIDGET</i>  <tt>xview</tt><p>
<dd>Returns a list containing two elements. The elements are a fractions
between 0.0 and 1.0 that define the position of the left and right
edges of
the visible part of the document as a fraction of the whole.<p>
<dt><i>WIDGET</i>  <tt>xview moveto</tt>  <i>FRACTION</i><p>
<dd>Adjusts the horizontal position of the document so that
<i>FRACTION</i> of the horizontal span of the document is off-screen
to the left.<p>
<dt><i>WIDGET</i>  <tt>xview scroll</i>  <i>NUMBER  WHAT</i><p>
<dd>
Shifts the view in the window left or right according to
<i>NUMBER</i> and <i>WHAT</i>.   <i>NUMBER</i> is an integer
and <i>WHAT</i> is either <tt>units</tt> or <tt>pages</tt>.<p>
</dl>
<dt><i>WIDGET</i>  <tt>yview</tt> <i>args...</i><p>
<dd>Used to control the vertical position of the document.<p>
<dl>
<dt><i>WIDGET</i>  <tt>yview</tt><p>
<dd>Returns a list containing two elements. The elements are a fractions
between 0.0 and 1.0 that define the position of the top and bottom
edges of
the visible part of the document as a fraction of the whole.<p>
<dt><i>WIDGET</i>  <tt>yview</tt>  <i>NAME</i><p>
<dd>Adjusts the vertical position of the document so that the tag
``<tt><a name=</tt><i>NAME</i><tt>></tt>'' is on screen,
and preferably near the top of the screen.<p>
<dt><i>WIDGET</i>  <tt>yview moveto</tt>  <i>FRACTION</i><p>
<dd>Adjusts the horizontal position of the document so that
<i>FRACTION</i> of the vertical span of the document is off-screen
above the visible region.<p>
<dt><i>WIDGET</i>  <tt>xview scroll</i> <i>NUMBER WHAT</i><p>
<dd>
Shifts the view in the window up or down according to
<i>NUMBER</i> and <i>WHAT</i>.   <i>NUMBER</i> is an integer
and <i>WHAT</i> is either <tt>units</tt> or <tt>pages</tt>.<p>
</dl>
</dl>
</body>
</html>
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