docs: def add_display_name(self, display_name):
          """Adds a display_name.
  
          arg:    display_name (displayText): the new display name
          raise:  InvalidArgument - ``display_name`` is invalid
          raise:  NoAccess - ``Metadata.isReadOnly()`` is ``true``
          raise:  NullArgument - ``display_name`` is ``null``
          *compliance: mandatory -- This method must be implemented.*
  
          """
          if self.get_display_names_metadata().is_read_only():
              raise NoAccess()
          if not isinstance(display_name, DisplayText):
              raise InvalidArgument('display_name must be instance of DisplayText')
          self.add_or_replace_value('displayNames', display_name)