code: def validate_properties_exist(self, classname, property_names):
          
          schema_element = self.get_element_by_class_name(classname)
  
          requested_properties = set(property_names)
          available_properties = set(schema_element.properties.keys())
          non_existent_properties = requested_properties - available_properties
          if non_existent_properties:
              raise InvalidPropertyError(
                  u'Class "{}" does not have definitions for properties "{}": '
                  u'{}'.format(classname, non_existent_properties, property_names))
docs: Validate that the specified property names are indeed defined on the given class.