I would like to have a way to group the nodes visually (this is only to
make it easier to look at the graph).
This would allow the user to easily see which nodes are related.
This means that the grouping should be visible through something like
color coding.
I tried the GMF's Node grouping feature but that's not what I wanted.
GMF grouping simply groups the nodes so that they can be moved
together. It does not add any visual clues showing that the nodes are
related.