NAME

       itclvars - variables used by [incr Tcl]
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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 "backward-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-qualified  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  encapsulation,  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(3itcl)