-Q10.C.5- use Tk in a subwindow of a non-Tk X11 application?

From: -X-  How, in Tk, can I XXX:

A10.C.5. From faustus@CS.Berkeley.EDU (Wayne A. Christopher):

[C]reate the Tk toplevel window but don't map it (wm withdraw).  Then
re-parent the window to be a subwindow of your other one and then map
it.  I have done this when the Tk application is a separate process,
but if it's the same process I think you will get into trouble with the
event loop, since each toolkit wants control.