on-focus in frame:basic-mixin

Called when a window receives or loses the keyboard focus. If the argument is #t, the keyboard focus was received, otherwise it was lost.

Note that under X, keyboard focus can move to the menu bar when the user is selecting a menu item.

• (send a-frame:basic-mixin on-focus on?) -> void
     on? : boolean

  Does nothing.

  Calls set-active-frame with this.