[I tried to post this before, but I don't think it posted.  My apologies 
if you get it twice. --BST]

 Does the ACL/Win Common Graphics library support the creation of 
aggregate widget types?  I know that the tab-control widget falls under 
this category, but support for that specific widget seems to be 
hard-wired into the other widgets. Or is that not true? 

By "aggregate widget type" I mean a widget which is a container for other 
widgets, and which can support functionality that depends on the 
coordinated activity of the widgets it contains.