show in frame:basic-mixin

Shows or hides a window.

The visibility of a window can be changed by the user clicking the window's close box, for example, and such changes do not go through this method; use on-superwindow-show or on-close to monitor visibility changes.

• (send a-frame:basic-mixin show on? void
     on? : boolean

  Calls the super method.

  When on? is #t, inserts the frame into the frame group and when it is #f, removes the frame from the group.