use of drawing area

[Andy Gilman <amgilman myfairpoint net>]

I am (still) a newbie at gtkmm and have been experimenting with 
cairomm.  In the tutorial the graphics are added to the window through a 
drawing area.  When I do this, I cannot add other widgets to the window 
(labels/buttons).  However, if I add the graphics directly to the window 
(that is the "on_draw" function applies to the window itself), it is 
possible to add other widgets (in an eventbox).

So:  my questions are these:  What is the advantage of using a drawing 
area for adding graphics (in this case custom decoration)?  and Is there 
some way to add widgets to a window that contains a drawingarea that I 
have missed.

Thanks.

Andy Gilman