Instance Data
All the variables of an instance are stored in a global associative array with the same name as the widget.
tixOnOff .onoff -text {Yes No} -value on
.onoff(-text) = {Yes No}
.onoff(-value) = on
Accessing the instance data in a method:
proc tixOnOff:toggle {w} {
upvar #0 $w data
if {$data(-value) == “on”} {
set data(-value) off
...
}