EDIT

Probably we need these for both, vocabularies and lists/trees/graphs.

As an example: structures which are more modifiers should all be handled in 1 vocabulary. However, we want to distinguish structures of type "temporal modifier", "structural modifier", "spatial modifier" and "contitional modifier".

Also in a tree it which is used e.g. for ordering it should be possible to put them all in 1 tree (otherwise common ordering is difficult) but to groups them (for better overview).

It needs to be discussed if we handle this by a flag, a special termtype, ... (in vocabularies) and in trees by flag or by leaving the term out (and instead use a i18n label only? The later seems to require lot of duplicated data structure so maybe not so good.