Is it possible to define navigations not only on “static”, vocabulary bound fields but also on “computed” field.

The concrete example is a migration vrom ELO where i have a virtual hierarchy containing some fix levels that may be bound to an hierarchy BUT also a level that extracts the year from the document creation date. Seems this is not possible directly in nuxeo?

Wouldn't it be a great feature to define a hierarchy level on a plain expression, not only a field of type “vocab”?