Exclusions in expand command

Peter yesterday lay a finger in the wound when asking about exclusion patterns in expansion. Maybe we can incorporate this in the command syntax. Think of something like this:

grid = yasp, ug | expand
degree = 2, 3 | expand exclude (grid=yasp, degree=3)

This would, after (or during, need to check) expansion delete all configurations that use the excluded combination of grid=yasp and degree=3 (as conforming Q3 elements are not implemented)

I am not entirely happy with it, but it would work.