Grouping features

It would be nice if there were some concept of (nested) groups, which could be displayed in various ways, e.g. using boxes, consistent colors, or similar, depending on the requirements of the application at hand. The terms resulting from an application of the ε-δ-rule are canonical examples of where such features might be useful, although other applications can be conceived.

As a further development, it would be great if such boxes could be collapsed to a single node, hiding all internal structure, and on the other way, could be expanded to fill the whole screen, hiding all other nodes. This would allow for graph manipulations on many levels, reducing the possibilities of accidents.