code: def _add_offsets_to_token_nodes(self):
          
          for edge_index in self._textual_relation_ids:
              token_node_index = self.edges[edge_index].source
              self.nodes[token_node_index].onset = self.edges[edge_index].onset
              self.nodes[token_node_index].offset = self.edges[edge_index].offset
docs: Adds primary text string onsets/offsets to all nodes that represent
          tokens. In SaltDocuments, this data was stored in TextualRelation
          edges only.