20. The method of claim 19 , wherein a subtree of the selected candidate tree comprises a location within the selected candidate tree and all internal and terminal nodes emanating from the location, and wherein modifying the selected candidate tree comprises: removing a subtree of the selected candidate tree associated with one location; inserting a new internal node into the selected candidate tree at said location; associating one of a horizontal division and a vertical division with the new internal node; inserting a new terminal node into the selected candidate tree emanating from the new internal node; associating the new terminal node with the subsequent graphic assembly; and inserting the subtree into the selected candidate tree, said subtree emanating from the new internal node.
19. The method of claim 6 , further comprising modifying the selected candidate tree to form at least one alternate candidate tree.