Add/substruct a whole collection into/from another

[andr]

This would add flexibility to collections. For example, now it is impossible to get a list of films which belong to collection A or collection B. If it was possible to create collection AplusB = A + B, this would allow getting such a list. YouTube playlists have similar functionality

[andr]

After I posted the suggestion, I found another topic with the same idea: viewtopic.php?f=8&t=6726