docs: def broadcast_definition(cast_name, onto_name):
      """
      Return the definition of a broadcast as an object with keys
      "cast", "onto", "cast_on", "onto_on", "cast_index", and "onto_index".
      These are the same as the arguments to the ``broadcast`` function.
  
      """
      if not orca.is_broadcast(cast_name, onto_name):
          abort(404)
  
      b = orca.get_broadcast(cast_name, onto_name)
  
      return jsonify(
          cast=b.cast, onto=b.onto, cast_on=b.cast_on, onto_on=b.onto_on,
          cast_index=b.cast_index, onto_index=b.onto_index)