-Q10.C.1- get an application to also use libXt?

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

A10.C.1. Tk2.1 and Xt have different X connections, and XtAppNextEvent will
block is there is nothing coming from the X connection.  One way
of fixing this is get the connection number of Tk using

   ConnectionNumber(Tk_Display(tk_window));

and using XtAddInput to register this with the Xt event handler.  The
callback procedure for XtAddInput wrapper procedure that runs
Tk_OneEvent(1).  There might be problems with Tk file sources which
aren't registered with Xt.

Thanks to joe@astro.as.utexas.edu (Joe Wang) for this information.