docs: def get_alt_texts_metadata(self):
          """Gets the metadata for all alt_texts.
  
          return: (osid.Metadata) - metadata for the alt_texts
          *compliance: mandatory -- This method must be implemented.*
  
          """
          metadata = dict(self._alt_texts_metadata)
          metadata.update({'existing_string_values': [t['text'] for t in self.my_osid_object_form._my_map['altTexts']]})
          return Metadata(**metadata)