itclvars(n) \[incr Tcl] itclvars(n)

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# [NAME](#NAME)

itclvars - variables used by \[incr Tcl]

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# [DESCRIPTION](#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**](#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**](#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**](#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**](#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](#KEYWORDS)

itcl, variables

3.0 itcl

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Document: itclvars(n) from tcl 9.1.0-r0 (Chainguard OS)
Source: https://downloads.sourceforge.net/project/tcl/Tcl/9.1.0/tcl9.1.0-src.tar.gz