code: def add_element(self, element, override=False):
          
          if issubclass(element, inline.InlineElement):
              dest = self.inline_elements
          elif issubclass(element, block.BlockElement):
              dest = self.block_elements
          else:
              raise TypeError(
                  'The element should be a subclass of either `BlockElement` or '
                  '`InlineElement`.'
              )
          if not override:
              dest[element.__name__] = element
          else:
              for cls in element.__bases__:
                  if cls in dest.values():
                      dest[cls.__name__] = element
                      break
              else:
                  dest[element.__name__] = element
docs: Add an element to the parser.
  
          :param element: the element class.
          :param override: whether to replace the default element based on.
  
          .. note:: If one needs to call it inside ``__init__()``, please call it after
               ``super().__init__()`` is called.