It would be nice to support clipping masks so that a complex drawing can be kept within certain bounds.
One way to do this is:
q # save the current graphics state
<x> <y> <width> <height> re # rectangle
W # modify clipping path
n # no-op - "don't paint the path"
The graphics state containing the original clipping mask can be retrieved later with a Q operator as per usual.
I don't think we have support for this now, but a patch would be welcome. Sorry we never responded to this request.
Adding myself to the issue