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itclvars(n)			  [incr Tcl]			   itclvars(n)

______________________________________________________________________________

NAME
       itclvars - variables used by [incr Tcl]
_________________________________________________________________

DESCRIPTION
       The following global variables are created and managed automatically by
       the [incr Tcl] library.	Except	where  noted  below,  these  variables
       should  normally	 be  treated as read-only by application-specific code
       and by users.

       itcl::library
	      When an interpreter  is  created,	 [incr Tcl]  initializes  this
	      variable	to  hold the name of a directory containing the system
	      library  of  [incr Tcl]	scripts.    The	  initial   value   of
	      itcl::library  is set from the ITCL_LIBRARY environment variable
	      if it exists, or from a compiled-in value otherwise.

       itcl::patchLevel
	      When an interpreter  is  created,	 [incr Tcl]  initializes  this
	      variable	to  hold  the current patch level for [incr Tcl].  For
	      example, the value "2.0p1" indicates [incr Tcl] version 2.0 with
	      the first set of patches applied.

       itcl::purist
	      When  an	interpreter  is	 created  containing  Tcl/Tk  and  the
	      [incr Tcl] namespace facility, this variable controls  a	"back‐
	      ward-compatibility" mode for widget access.

	      In  vanilla  Tcl/Tk,  there is a single pool of commands, so the
	      access command for a widget is the  same	as  the	 window	 name.
	      When a widget is created within a namespace, however, its access
	      command is installed in that namespace, and should  be  accessed
	      outside of the namespace using a qualified name.	For example,

		     namespace foo {
			 namespace bar {
			     button .b -text "Testing"
			 }
		     }
		     foo::bar::.b configure -background red
		     pack .b

	      Note that the window name ".b" is still used in conjunction with
	      commands like pack and destroy.  However, the access command for
	      the  widget  (i.e., name that appears as the first argument on a
	      command line) must be more specific.

	      The "winfo command" command can be used to query the fully-qual‐
	      ified access command for any widget, so one can write:

		     [winfo command .b] configure -background red

	      and  this	 is  good  practice  when  writing library procedures.
	      Also, in conjunction with the bind command, the "%q"  field  can
	      be used in place of "%W" as the access command:

		     bind Button <Key-Return> {%q flash; %q invoke}

	      While  this behavior makes sense from the standpoint of encapsu‐
	      lation, it causes problems with  existing	 Tcl/Tk	 applications.
	      Many  existing  applications  are written with bindings that use
	      "%W".  Many library procedures assume that the  window  name  is
	      the access command.

	      The  itcl::purist	 variable  controls  a	backward-compatibility
	      mode.  By default, this variable is "0", and the window name can
	      be  used	as  an	access	command	 in any context.  Whenever the
	      unknown procedure stumbles across a widget name, it simply  uses
	      "winfo  command"	to determine the appropriate command name.  If
	      this variable is set to "1", this backward-compatibility mode is
	      disabled.	 This gives better encapsulation, but using the window
	      name as the access command may lead to "invalid command" errors.

       itcl::version
	      When an interpreter  is  created,	 [incr Tcl]  initializes  this
	      variable to hold the version number of the form x.y.  Changes to
	      x represent major changes with  probable	incompatibilities  and
	      changes  to  y  represent	 small enhancements and bug fixes that
	      retain backward compatibility.

KEYWORDS
       itcl, variables

itcl				      3.0			   itclvars(n)
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