code: def get_span_offsets(docgraph, node_id):
      
      try:
          span = get_span(docgraph, node_id)
          # workaround for issue #138
          # TODO: when #138 is fixed, just take the first onset / last offset
          onsets, offsets = zip(*[docgraph.get_offsets(tok_node)
                                  for tok_node in span])
          return (min(onsets), max(offsets))
      except KeyError as _:
          raise KeyError("Node '{}' doesn't span any tokens.".format(node_id))
docs: returns the character start and end position of the span of text that
      the given node spans or dominates.
  
      Returns
      -------
      offsets : tuple(int, int)
          character onset and offset of the span