  The parent is the token that was specified when
<I>tkwin</I> was created, or NULL for main windows.
<P>
<B>Tk_Interp</B> returns the Tcl interpreter associated with a
<I>tkwin</I> or NULL if there is an error.
<P>
<B>Tk_Display</B> returns a pointer to the Xlib display structure
corresponding to <I>tkwin</I>.  <B>Tk_DisplayName</B> returns an
ASCII string identifying <I>tkwin</I>'s display.  <B>Tk_ScreenNumber</B>
returns the index of <I>tkwin</I>'s screen among all the screens
of <I>tkwin</I>'s display. 