Get and set the selected state of a gadget.
This attribute can be triggered by the user
clicking on the gadget (or using the keyboard),
depending on the input mode:
Set when lmb is pressed. Cleared when lmb is released.
Cleared when the gadget is selected and the mouse leaves
the gadget box. Set when the mouse reenters the gadget box.
Set when lmb is pressed.
Toggled when lmb is pressed.
Of course you may set this attribute yourself, e.g.
to adjust the state of a checkmark gadget.
A selected gadget will display its border reverse
and get the configured
This can be avoided using the Area.ShowSelState tag.