The schema definition should support complex types (map or list of map-like items).
Each map item can be multi valued, but cannot be complex itself (no support for lists of lists for instance).
The user selects "Complex property" in the type of property. That action makes a popup appear in which we can find the same kind of schema editor grid, but this time without ability to choose "Complex property"
These complex properties should be filtered from selectors presented for search (content views, advanced search form, virtual navigation)