+ segcmap S P...
+ Map segment S to colours using postscript commands P... (which
+ should be a postscript fragment to modify the graphics state,
+ typically `N setgray' or the like. This is used for the drawing
+ element Q (see below). S should be the bare segment (no movfeat).
+
+ segend S
+ Notes that segment S (which should not specify a movfeat) has
+ an end at this location. This is fed back from extractgraph's run
+ on a previous result of running layout, and used to determine where
+ to place the segment labels for E. NOT YET IMPLEMENTED
+