usual(3itk)

NAME
usual - access default option-handling commands
    for a mega-widget component

SYNOPSIS
usual ?tag? ?commands?

DESCRIPTION

The usual command is used outside of an [incr Tcl] class definition to define the usual set of option-handling commands for a component widget. Option-handling commands are used when a component is registered with the Archetype base class via the "itk_component add" method. They specify how the component's configuration options should be integrated into the composite option list for the mega-widget. Options can be kept, renamed, or ignored, as described in the Archetype man page.

It is tedious to include the same declarations again and again whenever components are added. The usual command allows a standard code fragment to be registered for each widget class, which is used by default to handle the options. All of the standard Tk widgets have usual declarations defined in the [incr Tk] library. Similar usual declarations should be created whenever a new mega-widget class is conceived. Only the most-generic options should be included in the usual declaration.

The tag name is usually the name of a widget class, which starts with a capital letter; however, any string registered here can be used later with the usual command described on the Archetype man page.

If the commands argument is specified, it is associated with the tag string, and can be accessed later via itk_component add.

If only the tag argument is specified, this command looks for an existing tag name and returns the commands associated with it. If there are no commands associated with tag, this command returns the null string.

If no arguments are specified, this command returns a list of all tag names previously registered.

EXAMPLE
Following is the usual declaration for the standard Tk button widget:
    itk::usual Button {
        keep -background -cursor -foreground -font
        keep -activebackground -activeforeground -disabledforeground
        keep -highlightcolor -highlightthickness
        rename -highlightbackground -background background Background
    }
Only the options that would be common to all buttons in a single mega-widget are kept or renamed. Options like "-text" that would be unique to a particular button are ignored.

KEYWORDS
itk, Archetype, component, mega-widget