code: public boolean isReferenceable( Name primaryType,
                                      Set<Name> mixinTypes ) {
          if (nodeTypeNamesThatAreReferenceable.contains(primaryType)) return true;
          if (mixinTypes != null) {
              for (Name mixinType : mixinTypes) {
                  if (nodeTypeNamesThatAreReferenceable.contains(mixinType)) return true;
              }
          }
          return false;
      }
docs: Determine if at least one of the named primary node type or mixin types is or subtypes the 'mix:referenceable' mixin type.
  
  @param primaryType the primary type name; may not be null
  @param mixinTypes the mixin type names; may be null or empty
  @return true if the primary node type is an 'mix:referenceable' node type (or subtype), or false otherwise