raw some background graphics to the window before the other visible objects draw themselves, or it may implement some special geometry behavior to arrange its children.</P>
<P>
The VisContent can have children. These children can be either standard visible objects or <EM>
composite</EM>
 visible objects. Composites, like the content, are allowed to have children. For efficiency, standard visible objects can not have children. Therefore, only leaf objects in the tree may be of <CODE>
VisClass</CODE>
.</P>
<P