docs: def _generate_list_heading(self):
          """
          Generate the list of heading links of page.
          """
  
          local = self.parser.find('body').first_result()
          id_container_heading_before = (
              AccessibleNavigationImplementation.ID_CONTAINER_HEADING_BEFORE
          )
          id_container_heading_after = (
              AccessibleNavigationImplementation.ID_CONTAINER_HEADING_AFTER
          )
          if local is not None:
              container_before = self.parser.find(
                  '#'
                  + id_container_heading_before
              ).first_result()
              if (container_before is None) and (self.elements_heading_before):
                  container_before = self.parser.create_element('div')
                  container_before.set_attribute(
                      'id',
                      id_container_heading_before
                  )
  
                  text_container_before = self.parser.create_element('span')
                  text_container_before.set_attribute(
                      'class',
                      AccessibleNavigationImplementation.CLASS_TEXT_HEADING
                  )
                  text_container_before.append_text(self.elements_heading_before)
  
                  container_before.append_element(text_container_before)
                  local.prepend_element(container_before)
              if container_before is not None:
                  self.list_heading_before = self.parser.find(
                      container_before
                  ).find_children('ol').first_result()
                  if self.list_heading_before is None:
                      self.list_heading_before = self.parser.create_element('ol')
                      container_before.append_element(self.list_heading_before)
  
              container_after = self.parser.find(
                  '#'
                  + id_container_heading_after
              ).first_result()
              if (container_after is None) and (self.elements_heading_after):
                  container_after = self.parser.create_element('div')
                  container_after.set_attribute('id', id_container_heading_after)
  
                  text_container_after = self.parser.create_element('span')
                  text_container_after.set_attribute(
                      'class',
                      AccessibleNavigationImplementation.CLASS_TEXT_HEADING
                  )
                  text_container_after.append_text(self.elements_heading_after)
  
                  container_after.append_element(text_container_after)
                  local.append_element(container_after)
              if container_after is not None:
                  self.list_heading_after = self.parser.find(
                      container_after
                  ).find_children('ol').first_result()
                  if self.list_heading_after is None:
                      self.list_heading_after = self.parser.create_element('ol')
                      container_after.append_element(self.list_heading_after)
          self.list_heading_added = True