---
name: "itclvars"
section: "3itcl"
platform: "linux"
package: "itcl3-doc"
version: "3.4.4-3"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/itclvars"
---

# itclvars(3itcl)

variables used by \[incr Tcl\]

```

```

## 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 "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