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+'\"
+'\" Copyright (c) 1993-1997 Bell Labs Innovations for Lucent Technologies
+'\" Copyright (c) 1997 Sun Microsystems, Inc.
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\" 
+'\" SCCS: @(#) namespace.n 1.9 97/08/13 17:08:25
+'\" 
+.so man.macros
+.TH namespace n 8.0 Tcl "Tcl Built-In Commands"
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+namespace \- create and manipulate contexts for commands and variables
+.SH SYNOPSIS
+\fBnamespace \fR?\fIoption\fR? ?\fIarg ...\fR?
+.BE
+
+.SH DESCRIPTION
+.PP
+The \fBnamespace\fR command lets you create, access, and destroy
+separate contexts for commands and variables.
+See the section \fBWHAT IS A NAMESPACE?\fR below
+for a brief overview of namespaces.
+The legal \fIoption\fR's are listed below.
+Note that you can abbreviate the \fIoption\fR's.
+.TP
+\fBnamespace children \fR?\fInamespace\fR? ?\fIpattern\fR?
+Returns a list of all child namespaces that belong to the
+namespace \fInamespace\fR.
+If \fInamespace\fR is not specified,
+then the children are returned for the current namespace.
+This command returns fully-qualified names,
+which start with \fB::\fR.
+If the optional \fIpattern\fR is given,
+then this command returns only the names that match the glob-style pattern.
+The actual pattern used is determined as follows:
+a pattern that starts with \fB::\fR is used directly,
+otherwise the namespace \fInamespace\fR
+(or the fully-qualified name of the current namespace)
+is prepended onto the the pattern.
+.TP
+\fBnamespace code \fIscript\fR
+Captures the current namespace context for later execution
+of the script \fIscript\fR.
+It returns a new script in which \fIscript\fR has been wrapped
+in a \fBnamespace code\fR command.
+The new script has two important properties.
+First, it can be evaluated in any namespace and will cause
+\fIscript\fR to be evaluated in the current namespace
+(the one where the \fBnamespace code\fR command was invoked).
+Second, additional arguments can be appended to the resulting script
+and they will be passed to \fIscript\fR as additional arguments.
+For example, suppose the command
+\fBset script [namespace code {foo bar}]\fR
+is invoked in namespace \fB::a::b\fR.
+Then \fBeval "$script x y"\fR
+can be executed in any namespace (assuming the value of
+\fBscript\fR has been passed in properly)
+and will have the same effect as the command
+\fBnamespace eval ::a::b {foo bar x y}\fR.
+This command is needed because
+extensions like Tk normally execute callback scripts
+in the global namespace.
+A scoped command captures a command together with its namespace context
+in a way that allows it to be executed properly later.
+See the section \fBSCOPED VALUES\fR for some examples
+of how this is used to create callback scripts.
+.TP
+\fBnamespace current\fR
+Returns the fully-qualified name for the current namespace.
+The actual name of the global namespace is ``''
+(i.e., an empty string),
+but this command returns \fB::\fR for the global namespace
+as a convenience to programmers.
+.TP
+\fBnamespace delete \fR?\fInamespace namespace ...\fR?
+Each namespace \fInamespace\fR is deleted
+and all variables, procedures, and child namespaces
+contained in the namespace are deleted.
+If a procedure is currently executing inside the namespace,
+the namespace will be kept alive until the procedure returns;
+however, the namespace is marked to prevent other code from
+looking it up by name.
+If a namespace doesn't exist, this command returns an error.
+If no namespace names are given, this command does nothing.
+.TP
+\fBnamespace eval\fR \fInamespace arg\fR ?\fIarg ...\fR?
+Activates a namespace called \fInamespace\fR and evaluates some code
+in that context.
+If the namespace does not already exist, it is created.
+If more than one \fIarg\fR argument is specified,
+the arguments are concatenated together with a space between each one
+in the same fashion as the \fBeval\fR command,
+and the result is evaluated.
+.br
+.sp
+If \fInamespace\fR has leading namespace qualifiers
+and any leading namespaces do not exist,
+they are automatically created.
+.TP
+\fBnamespace export \fR?\-\fBclear\fR? ?\fIpattern pattern ...\fR?
+Specifies which commands are exported from a namespace.
+The exported commands are those that can be later imported
+into another namespace using a \fBnamespace import\fR command.
+Both commands defined in a namespace and
+commands the namespace has previously imported
+can be exported by a namespace.
+The commands do not have to be defined
+at the time the \fBnamespace export\fR command is executed.
+Each \fIpattern\fR may contain glob-style special characters,
+but it may not include any namespace qualifiers.
+That is, the pattern can only specify commands
+in the current (exporting) namespace.
+Each \fIpattern\fR is appended onto the namespace's list of export patterns.
+If the \-\fBclear\fR flag is given,
+the namespace's export pattern list is reset to empty before any
+\fIpattern\fR arguments are appended.
+If no \fIpattern\fRs are given and the \-\fBclear\fR flag isn't given,
+this command returns the namespace's current export list.
+.TP
+\fBnamespace forget \fR?\fIpattern pattern ...\fR?
+Removes previously imported commands from a namespace.
+Each \fIpattern\fR is a qualified name such as
+\fBfoo::x\fR or \fBa::b::p*\fR.
+Qualified names contain \fB::\fRs and qualify a name
+with the name of one or more namespaces.
+Each \fIpattern\fR is qualified with the name of an exporting namespace
+and may have glob-style special characters in the command name
+at the end of the qualified name.
+Glob characters may not appear in a namespace name.
+This command first finds the matching exported commands.
+It then checks whether any of those those commands
+were previously imported by the current namespace.
+If so, this command deletes the corresponding imported commands. 
+In effect, this un-does the action of a \fBnamespace import\fR command.
+.TP
+\fBnamespace import \fR?\fB\-force\fR? ?\fIpattern\fR \fIpattern ...\fR?
+Imports commands into a namespace.
+Each \fIpattern\fR is a qualified name like
+\fBfoo::x\fR or \fBa::p*\fR.
+That is, it includes the name of an exporting namespace
+and may have glob-style special characters in the command name
+at the end of the qualified name.
+Glob characters may not appear in a namespace name.
+All the commands that match a \fIpattern\fR string
+and which are currently exported from their namespace
+are added to the current namespace.
+This is done by creating a new command in the current namespace
+that points to the exported command in its original namespace;
+when the new imported command is called, it invokes the exported command.
+This command normally returns an error
+if an imported command conflicts with an existing command.
+However, if the \-\fBforce\fR option is given,
+imported commands will silently replace existing commands.
+The \fBnamespace import\fR command has snapshot semantics:
+that is, only requested commands that are currently defined
+in the exporting namespace are imported.
+In other words, you can import only the commands that are in a namespace
+at the time when the \fBnamespace import\fR command is executed.
+If another command is defined and exported in this namespace later on,
+it will not be imported.
+.TP
+\fBnamespace inscope\fR \fInamespace arg\fR ?\fIarg ...\fR?
+Executes a script in the context of a particular namespace.
+This command is not expected to be used directly by programmers;
+calls to it are generated implicitly when applications
+use \fBnamespace code\fR commands to create callback scripts
+that the applications then register with, e.g., Tk widgets.
+The \fBnamespace inscope\fR command is much like the \fBnamespace eval\fR
+command except that it has \fBlappend\fR semantics
+and the namespace must already exist.
+It treats the first argument as a list,
+and appends any arguments after the first
+onto the end as proper list elements.
+\fBnamespace inscope ::foo a x y z\fR
+is equivalent to
+\fBnamespace eval ::foo [concat a [list x y z]]\fR
+This \fBlappend\fR semantics is important because many callback scripts
+are actually prefixes.
+.TP
+\fBnamespace origin \fIcommand\fR
+Returns the fully-qualified name of the original command
+to which the imported command \fIcommand\fR refers.
+When a command is imported into a namespace,
+a new command is created in that namespace
+that points to the actual command in the exporting namespace.
+If a command is imported into a sequence of namespaces
+\fIa, b,...,n\fR where each successive namespace
+just imports the command from the previous namespace,
+this command returns the fully-qualified name of the original command
+in the first namespace, \fIa\fR.
+If \fIcommand\fR does not refer to an imported command,
+the command's own fully-qualified name is returned.
+.TP
+\fBnamespace parent\fR ?\fInamespace\fR?
+Returns the fully-qualified name of the parent namespace
+for namespace \fInamespace\fR.
+If \fInamespace\fR is not specified,
+the fully-qualified name of the current namespace's parent is returned.
+.TP
+\fBnamespace qualifiers\fR \fIstring\fR
+Returns any leading namespace qualifiers for \fIstring\fR.
+Qualifiers are namespace names separated by \fB::\fRs.
+For the \fIstring\fR \fB::foo::bar::x\fR,
+this command returns \fB::foo::bar\fR,
+and for \fB::\fR it returns \fB``''\fR (an empty string).
+This command is the complement of the \fBnamespace tail\fR command.
+Note that it does not check whether the
+namespace names are, in fact,
+the names of currently defined namespaces.
+.TP
+\fBnamespace tail\fR \fIstring\fR
+Returns the simple name at the end of a qualified string.
+Qualifiers are namespace names separated by \fB::\fRs.
+For the \fIstring\fR \fB::foo::bar::x\fR,
+this command returns \fBx\fR,
+and for \fB::\fR it returns \fB``''\fR (an empty string).
+This command is the complement of the \fBnamespace qualifiers\fR command.
+It does not check whether the namespace names are, in fact,
+the names of currently defined namespaces.
+.TP
+\fBnamespace which\fR ?\-\fBcommand\fR? ?\-\fBvariable\fR? \fIname\fR
+Looks up \fIname\fR as either a command or variable
+and returns its fully-qualified name.
+For example, if \fIname\fR does not exist in the current namespace
+but does exist in the global namespace,
+this command returns a fully-qualified name in the global namespace.
+If the command or variable does not exist,
+this command returns an empty string.
+If no flag is given, \fIname\fR is treated as a command name.
+See the section \fBNAME RESOLUTION\fR below for an explanation of
+the rules regarding name resolution.
+
+.SH "WHAT IS A NAMESPACE?"
+.PP
+A namespace is a collection of commands and variables.
+It encapsulates the commands and variables to ensure that they
+won't interfere with the commands and variables of other namespaces.
+Tcl has always had one such collection,
+which we refer to as the \fIglobal namespace\fR.
+The global namespace holds all global variables and commands.
+The \fBnamespace eval\fR command lets you create new namespaces.
+For example,
+.CS
+\fBnamespace eval Counter {
+    namespace export Bump
+    variable num 0
+
+    proc Bump {} {
+        variable num
+        incr num
+    }
+}\fR
+.CE
+creates a new namespace containing the variable \fBnum\fR and
+the procedure \fBBump\fR.
+The commands and variables in this namespace are separate from
+other commands and variables in the same program.
+If there is a command named \fBBump\fR in the global namespace,
+for example, it will be different from the command \fBBump\fR
+in the \fBCounter\fR namespace.
+.PP
+Namespace variables resemble global variables in Tcl.
+They exist outside of the procedures in a namespace
+but can be accessed in a procedure via the \fBvariable\fR command,
+as shown in the example above.
+.PP
+Namespaces are dynamic.
+You can add and delete commands and variables at any time,
+so you can build up the contents of a
+namespace over time using a series of \fBnamespace eval\fR commands.
+For example, the following series of commands has the same effect
+as the namespace definition shown above:
+.CS
+\fBnamespace eval Counter {
+    variable num 0
+    proc Bump {} {
+        variable num
+        return [incr num]
+    }
+}
+namespace eval Counter {
+    proc test {args} {
+        return $args
+    }
+}
+namespace eval Counter {
+    rename test ""
+}\fR
+.CE
+Note that the \fBtest\fR procedure is added to the \fBCounter\fR namespace,
+and later removed via the \fBrename\fR command.
+.PP
+Namespaces can have other namespaces within them,
+so they nest hierarchically.
+A nested namespace is encapsulated inside its parent namespace
+and can not interfere with other namespaces.
+
+.SH "QUALIFIED NAMES"
+.PP
+Each namespace has a textual name such as
+\fBhistory\fR or \fB::safe::interp\fR.
+Since namespaces may nest,
+qualified names are used to refer to
+commands, variables, and child namespaces contained inside namespaces.
+Qualified names are similar to the hierarchical path names for
+Unix files or Tk widgets,
+except that \fB::\fR is used as the separator
+instead of \fB/\fR or \fB.\fR.
+The topmost or global namespace has the name ``'' (i.e., an empty string),
+although \fB::\fR is a synonym.
+As an example, the name \fB::safe::interp::create\fR
+refers to the command \fBcreate\fR in the namespace \fBinterp\fR
+that is a child of of namespace \fB::safe\fR,
+which in turn is a child of the global namespace \fB::\fR.
+.PP
+If you want to access commands and variables from another namespace,
+you must use some extra syntax.
+Names must be qualified by the namespace that contains them.
+From the global namespace,
+we might access the \fBCounter\fR procedures like this:
+.CS
+\fBCounter::Bump 5
+Counter::Reset\fR
+.CE
+We could access the current count like this:
+.CS
+\fBputs "count = $Counter::num"\fR
+.CE
+When one namespace contains another, you may need more than one
+qualifier to reach its elements.
+If we had a namespace \fBFoo\fR that contained the namespace \fBCounter\fR,
+you could invoke its \fBBump\fR procedure
+from the global namespace like this:
+.CS
+\fBFoo::Counter::Bump 3\fR
+.CE
+.PP
+You can also use qualified names when you create and rename commands.
+For example, you could add a procedure to the \fBFoo\fR
+namespace like this:
+.CS
+\fBproc Foo::Test {args} {return $args}\fR
+.CE
+And you could move the same procedure to another namespace like this:
+.CS
+\fBrename Foo::Test Bar::Test\fR
+.CE
+.PP
+There are a few remaining points about qualified names
+that we should cover.
+Namespaces have nonempty names except for the global namespace.
+\fB::\fR is disallowed in simple command, variable, and namespace names
+except as a namespace separator.
+Extra \fB:\fRs in a qualified name are ignored;
+that is, two or more \fB:\fRs are treated as a namespace separator.
+A trailing \fB::\fR in a qualified variable or command name
+refers to the variable or command named {}.
+However, a trailing \fB::\fR in a qualified namespace name is ignored.
+
+.SH "NAME RESOLUTION"
+.PP
+In general, all Tcl commands that take variable and command names
+support qualified names.
+This means you can give qualified names to such commands as
+\fBset\fR, \fBproc\fR, \fBrename\fR, and \fBinterp alias\fR.
+If you provide a fully-qualified name that starts with a \fB::\fR,
+there is no question about what command, variable, or namespace
+you mean.
+However, if the name does not start with a \fB::\fR
+(i.e., is \fIrelative\fR), 
+Tcl follows a fixed rule for looking it up:
+Command and variable names are always resolved
+by looking first in the current namespace,
+and then in the global namespace.
+Namespace names, on the other hand, are always resolved
+by looking in only the current namespace.
+.PP
+In the following example,
+.CS
+\fBset traceLevel 0
+namespace eval Debug {
+    printTrace $traceLevel
+}\fR
+.CE
+Tcl looks for \fBtraceLevel\fR in the namespace \fBDebug\fR
+and then in the global namespace.
+It looks up the command \fBprintTrace\fR in the same way.
+If a variable or command name is not found in either context,
+the name is undefined.
+To make this point absolutely clear, consider the following example:
+.CS
+\fBset traceLevel 0
+namespace eval Foo {
+    variable traceLevel 3
+
+    namespace eval Debug {
+        printTrace $traceLevel
+    }
+}\fR
+.CE
+Here Tcl looks for \fBtraceLevel\fR first in the namespace \fBFoo::Debug\fR.
+Since it is not found there, Tcl then looks for it 
+in the global namespace.
+The variable \fBFoo::traceLevel\fR is completely ignored
+during the name resolution process.
+.PP
+You can use the \fBnamespace which\fR command to clear up any question
+about name resolution.
+For example, the command:
+.CS
+\fBnamespace eval Foo::Debug {namespace which \-variable traceLevel}\fR
+.CE
+returns \fB::traceLevel\fR.
+On the other hand, the command,
+.CS
+\fBnamespace eval Foo {namespace which \-variable traceLevel}\fR
+.CE
+returns \fB::Foo::traceLevel\fR.
+.PP
+As mentioned above,
+namespace names are looked up differently
+than the names of variables and commands.
+Namespace names are always resolved in the current namespace.
+This means, for example,
+that a \fBnamespace eval\fR command that creates a new namespace
+always creates a child of the current namespace
+unless the new namespace name begins with a \fB::\fR.
+.PP
+Tcl has no access control to limit what variables, commands,
+or namespaces you can reference.
+If you provide a qualified name that resolves to an element
+by the name resolution rule above,
+you can access the element.
+.PP
+You can access a namespace variable
+from a procedure in the same namespace
+by using the \fBvariable\fR command.
+Much like the \fBglobal\fR command,
+this creates a local link to the namespace variable.
+If necessary, it also creates the variable in the current namespace
+and initializes it.
+Note that the \fBglobal\fR command only creates links
+to variables in the global namespace.
+It is not necessary to use a \fBvariable\fR command
+if you always refer to the namespace variable using an
+appropriate qualified name.
+
+.SH "IMPORTING COMMANDS"
+.PP
+Namespaces are often used to represent libraries.
+Some library commands are used so frequently
+that it is a nuisance to type their qualified names.
+For example, suppose that all of the commands in a package
+like BLT are contained in a namespace called \fBBlt\fR.
+Then you might access these commands like this:
+.CS
+\fBBlt::graph .g \-background red
+Blt::table . .g 0,0\fR
+.CE
+If you use the \fBgraph\fR and \fBtable\fR commands frequently,
+you may want to access them without the \fBBlt::\fR prefix.
+You can do this by importing the commands into the current namespace,
+like this:
+.CS
+\fBnamespace import Blt::*\fR
+.CE
+This adds all exported commands from the \fBBlt\fR namespace
+into the current namespace context, so you can write code like this:
+.CS
+\fBgraph .g \-background red
+table . .g 0,0\fR
+.CE
+The \fBnamespace import\fR command only imports commands
+from a namespace that that namespace exported
+with a \fBnamespace export\fR command.
+.PP
+Importing \fIevery\fR command from a namespace is generally
+a bad idea since you don't know what you will get.
+It is better to import just the specific commands you need.
+For example, the command
+.CS
+\fBnamespace import Blt::graph Blt::table\fR
+.CE
+imports only the \fBgraph\fR and \fBtable\fR commands into the
+current context.
+.PP
+If you try to import a command that already exists, you will get an
+error.  This prevents you from importing the same command from two
+different packages.  But from time to time (perhaps when debugging),
+you may want to get around this restriction.  You may want to
+reissue the \fBnamespace import\fR command to pick up new commands
+that have appeared in a namespace.  In that case, you can use the
+\fB\-force\fR option, and existing commands will be silently overwritten:
+.CS
+\fBnamespace import \-force Blt::graph Blt::table\fR
+.CE
+If for some reason, you want to stop using the imported commands,
+you can remove them with an \fBnamespace forget\fR command, like this:
+.CS
+\fBnamespace forget Blt::*\fR
+.CE
+This searches the current namespace for any commands imported from \fBBlt\fR.
+If it finds any, it removes them.  Otherwise, it does nothing.
+After this, the \fBBlt\fR commands must be accessed with the \fBBlt::\fR
+prefix.
+.PP
+When you delete a command from the exporting namespace like this:
+.CS
+\fBrename Blt::graph ""\fR
+.CE
+the command is automatically removed from all namespaces that import it.
+
+.SH "EXPORTING COMMANDS"
+You can export commands from a namespace like this:
+.CS
+\fBnamespace eval Counter {
+    namespace export Bump Reset
+    variable num 0
+    variable max 100
+
+    proc Bump {{by 1}} {
+        variable num
+        incr num $by
+        check
+        return $num
+    }
+    proc Reset {} {
+        variable num
+        set num 0
+    }
+    proc check {} {
+        variable num
+        variable max
+        if {$num > $max} {
+            error "too high!"
+        }
+    }
+}\fR
+.CE
+The procedures \fBBump\fR and \fBReset\fR are exported,
+so they are included when you import from the \fBCounter\fR namespace,
+like this:
+.CS
+\fBnamespace import Counter::*\fR
+.CE
+However, the \fBcheck\fR procedure is not exported,
+so it is ignored by the import operation.
+.PP
+The \fBnamespace import\fR command only imports commands
+that were declared as exported by their namespace.
+The \fBnamespace export\fR command specifies what commands
+may be imported by other namespaces.
+If a \fBnamespace import\fR command specifies a command
+that is not exported, the command is not imported.
+
+.SH "SEE ALSO"
+variable(n)
+
+.SH KEYWORDS
+exported, internal, variable