code: def add_class_properties_xsd(self, tb, cls):
          
          for p in class_mapper(cls).iterate_properties:
              if isinstance(p, ColumnProperty):
                  self.add_column_property_xsd(tb, p)
          if self.sequence_callback:
              self.sequence_callback(tb, cls)
docs: Add the XSD for the class properties to the ``TreeBuilder``. And
          call the user ``sequence_callback``.