docs: def add_accessibility_type(self, accessibility_type=None):
          """Adds an accessibility type.
  
          Multiple types can be added.
  
          :param accessibility_type: a new accessibility type
          :type accessibility_type: ``osid.type.Type``
          :raise: ``InvalidArgument`` -- ``accessibility_type`` is invalid
          :raise: ``NoAccess`` -- ``Metadata.isReadOnly()`` is ``true``
          :raise: ``NullArgument`` -- ``accessibility_t_ype`` is ``null``
  
          *compliance: mandatory -- This method must be implemented.*
  
          """
          if accessibility_type is None:
              raise NullArgument()
          metadata = Metadata(**settings.METADATA['accessibility_type'])
          if metadata.is_read_only():
              raise NoAccess()
          if self._is_valid_input(accessibility_type, metadata, array=False):
              self._my_map['accessibilityTypeIds'].append(accessibility_type._my_map['id'])
              # REALLY?  This assumes that all accessibility_type arguments
              # will be Types that have come from Handcar.  Perhaps?
          else:
              raise InvalidArgument