I have in mind options as in the Calendar Tool. Details to come.
The following list looks like an color option thing, where the `Format->Color menu applies to the current canvas selection(s); node background, node border, node label, edge line, edge arrowhead, edge label. Hmm, maybe not, since we want consistent menu behavior, and the ability to set the current color, but probably should be able to do so for a particular context.
Submenu (or tab pane) details:
Node Shape -- circle, elipse, other
Edge Shape -- curve, multiline
Ungroup -- enabled when a grouped node or edge is selected
Regroup -- enabled when one or more ungrouped components of a previously
ungrouped node or edge is selected
Dimensions ... -- diameter, margin
Font ... -- the normal font stuff
Other options: