code: def sentence(self):
          
          if self._sentence is None:
              sentences = self._element.xpath('sentence/text()')
              if len(sentences) > 0:
                  self._sentence = self._coref.document.get_sentence_by_id(int(sentences[0]))
          return self._sentence
docs: The sentence related to this mention
  
          :getter: returns the sentence this mention relates to
          :type: corenlp_xml.document.Sentence