docs: def add_column_property_xsd(self, tb, column_property):
          """ Add the XSD for a column property to the ``TreeBuilder``. """
          if len(column_property.columns) != 1:
              raise NotImplementedError  # pragma: no cover
          column = column_property.columns[0]
          if column.primary_key and not self.include_primary_keys:
              return
          if column.foreign_keys and not self.include_foreign_keys:
              if len(column.foreign_keys) != 1:  # pragma: no cover
                  # FIXME understand when a column can have multiple
                  # foreign keys
                  raise NotImplementedError()
              return
          attrs = {'name': column_property.key}
          self.add_column_xsd(tb, column, attrs)