code: def divide(self, layer=WORDS, by=SENTENCES):
          
          if not self.is_tagged(layer):
              self.tag(layer)
          if not self.is_tagged(by):
              self.tag(by)
          return divide(self[layer], self[by])
docs: Divide the Text into pieces by keeping references to original elements, when possible.
          This is not possible only, if the _element_ is a multispan.
  
          Parameters
          ----------
  
          element: str
              The element to collect and distribute in resulting bins.
          by: str
              Each resulting bin is defined by spans of this element.
  
          Returns
          -------
          list of (list of dict)