code: def add(self, doc):
          
          array = doc.to_array(self.attrs)
          if len(array.shape) == 1:
              array = array.reshape((array.shape[0], 1))
          self.tokens.append(array)
          spaces = doc.to_array(SPACY)
          assert array.shape[0] == spaces.shape[0]
          spaces = spaces.reshape((spaces.shape[0], 1))
          self.spaces.append(numpy.asarray(spaces, dtype=bool))
          self.strings.update(w.text for w in doc)
docs: Add a doc's annotations to the binder for serialization.