I recently discovered a use for how data structures in gops bleed through to the parent. test.pd demonstrates a gui object that jumps out of its gop box when clicked.
This technique is limited, though, because you can't manipulate the grob with the mouse once it goes outside the gop box; so a youtube type volume slider would have to be drawn within gop constraints to be usable. (The other drawback is obvious once you open the abstraction.)
-Jonathan