code: def get_conano_units(docgraph, data=True, conano_namespace='conano'):
      
      for unit_id in sorted(select_nodes_by_layer(docgraph, conano_namespace+':unit'),
                            key=natural_sort_key):
          yield (unit_id, get_span(docgraph, unit_id)) if data else (unit_id)
docs: yield all Conano units that occur in the given document graph,
      sorted by their unit ID. int(ernal) and ext(ernal) count as distinct units.
  
      Parameters
      ----------
      docgraph : DiscourseDocumentGraph
          a document graph which contains Conano annotations
      data : bool
          If True (default), yields (node ID, list of tokens)
          tuples. If False, yields just unit IDs.
      conano_namespace : str
          The namespace that the Conano annotations use (default: conano)
  
      Yields
      ------
      relations : str or (str, str, list of str) tuples
          If data=False, this will just yield node IDs of the nodes that
          directly dominate an RST relation. If data=True, this yields
          tuples of the form: (node ID, relation name, list of tokens that this
          relation spans).