code: def add(self, element):
          
          if isinstance(element, list):
              for e in element:
                  if isinstance(e, Label):
                      self.labels.append(e)
                  else:
                      self.elements.append(e)
          else:
              if isinstance(element, Label):
                  self.labels.append(element)
              else:
                  self.elements.append(element)
          self._bb_valid = False
          return self
docs: Add a new element or list of elements to this cell.
  
          Parameters
          ----------
          element : object, list
              The element or list of elements to be inserted in this cell.
  
          Returns
          -------
          out : ``Cell``
              This cell.