A checkbutton widget is used to show or change a setting. It has two states, selected and deselected. The state of the checkbutton may be linked to a Tcl variable.
In addition to the standard cget, configure, instate, and state commands, checkbuttons support the following additional widget commands:
The widget does not respond to user input if the disabled state is set. The widget sets the selected state whenever the linked -variable is set to the widget's -onvalue, and clears it otherwise. The widget sets the alternate state whenever the linked -variable is unset. (The alternate state may be used to indicate a ``tri-state'' or ``indeterminate'' selection.)