How do you tell another process which widget to put into a plug?

[sandmanbig <sandmanbig gmail com>]

Hello, this is my first post to the group. Nice to meet you all.

I am trying to write a global menu bar app so that I can learn how
they work. I know how to obtain the active window, but according to
the Xembed spec, the client (the app that has the menubar) creates a
GtkPlug and places the widget into that plug.

My question is, how do I tell process B that I want to embed its
menubar using GtkSocket and GtkPlug in process A? I have found a
handful of articles saying how to embed an entire app into a window,
but I have not been able to find anything about how to embed a certain
widget.

The Xembed spec specifically says the way that works is unspecified,
and I have not found a solution in the ICCCM, either. I have tried
libwnck, Xlib, etc, with no success. I haven't found any example for
specifically embedding a particular widget from a foreign window
online. I've spent a long time researching this, and I'm not getting
anywhere.

Perhaps I'm approaching this the wrong way. I am using C and Gtk+ 3.
If anybody can offer any advice, I'd greatly appreciate it.

Thank you!