Compliance levels schema for Simple features GML 3.2 Profile
Copyright (c) 2011 Open Geospatial Consortium.
Level 0 = no complex-valued properties and minOccurs,maxOccurs
have a value domain of 0 or 1
Level 1 = complex-valued properties with no restriction on
minOccurs and maxOccurs
Level 2 = no restrictions on type of non-spatial scalar properties
but must only support spatial properties declared in
clause 8