code: def control(self) -> Optional[HTMLElement]:
          
          id = self.getAttribute('for')
          if id:
              if self.ownerDocument:
                  return self.ownerDocument.getElementById(id)
              elif isinstance(id, str):
                  from wdom.document import getElementById
                  return getElementById(id)
              else:
                  raise TypeError('"for" attribute must be string')
          return None
docs: Return related HTMLElement object.