code: def format_registryfield_nodes(field_name, field, field_id, state, lineno):
      from lsst.pex.config.registry import ConfigurableWrapper
      choice_dl = nodes.definition_list()
      for choice_value, choice_class in field.registry.items():
          if hasattr(choice_class, '__module__') \
                  and hasattr(choice_class, '__name__'):
              name = '.'.join((choice_class.__module__, choice_class.__name__))
          elif isinstance(choice_class, ConfigurableWrapper):
              name = '.'.join((choice_class._target.__class__.__module__,
                               choice_class._target.__class__.__name__))
          else:
              name = '.'.join((choice_class.__class__.__module__,
                               choice_class.__class__.__name__))
          item = nodes.definition_list_item()
          item_term = nodes.term()
          item_term += nodes.literal(text=repr(choice_value))
          item += item_term
          item_definition = nodes.definition()
          def_para = nodes.paragraph()
          def_para += pending_task_xref(rawsource=name)
          item_definition += def_para
          item += item_definition
          choice_dl.append(item)
      choices_node = nodes.definition_list_item()
      choices_node.append(nodes.term(text='Choices'))
      choices_definition = nodes.definition()
      choices_definition.append(choice_dl)
      choices_node.append(choices_definition)
      field_type_item = nodes.definition_list_item()
      field_type_item.append(nodes.term(text="Field type"))
      field_type_item_content = nodes.definition()
      field_type_item_content_p = nodes.paragraph()
      if field.multi:
          multi_text = "Multi-selection "
      else:
          multi_text = "Single-selection "
      field_type_item_content_p += nodes.Text(multi_text, multi_text)
      field_type_item_content_p += make_python_xref_nodes_for_type(
          type(field),
          state,
          hide_namespace=True)[0].children[0]
      if field.optional:
          field_type_item_content_p += nodes.Text(' (optional)', ' (optional)')
      field_type_item_content += field_type_item_content_p
      field_type_item += field_type_item_content
      dl = nodes.definition_list()
      dl += create_default_item_node(field, state)
      dl += field_type_item
      dl += choices_node
      desc_node = create_description_node(field, state)
      title = create_title_node(field_name, field, field_id, state, lineno)
      return [title, dl, desc_node]