Why is GtkPlug a GtkWindow?

["Craig S. Kaplan" <csk cs washington edu>]

Question about GtkPlug:

Why must GtkPlug inherit from GtkWindow?  And why must it be
a toplevel window, for that matter?  It seems like making inherit
from GtkWidget (or maybe GtkBin) allows for a much wider range
of applications, where I can embed my GtkPlug object deep 
inside some complicated layout, surrounded by other GTK widgets
(or is this possible and non-obvious).

I don't know much about X, so if there's some gnarly X-related
reason why GtkPlug must be a GtkWindow, I'd love to hear about it.

Thanks!

--
Craig.              http://www.cs.washington.edu/homes/csk/
Counterfactuals: what would the world be like without them?