+ /* Vertical order is the level position (rank) of the summary node of an
+ inner subgraph, if this subgraph is folded. We can also specify
+ level: int. The level is only recognized, if an automatical layout is
+ calculated. */
+ int vertical_order;
+
+ /* Horizontal order is the horizontal position of the summary node within
+ a level. The nodes which are specified with horizontal positions are
+ ordered according to these positions within the levels. The nodes which
+ do not have this attribute are inserted into this ordering by the
+ crossing reduction mechanism. Note that connected components are
+ handled separately, thus it is not possible to intermix such components
+ by specifying a horizontal order. If the algorithm for downward laid
+ out trees is used, the horizontal order influences only the order of
+ the child nodes at a node, but not the order of the whole level. */
+ int horizontal_order;