docs: def buses_of_vlvl(network, voltage_level):
      """ Get bus-ids of given voltage level(s).
  
      Parameters
      ----------
      network : :class:`pypsa.Network
          Overall container of PyPSA
      voltage_level: list
  
      Returns
      -------
      list
          List containing bus-ids.
      """
  
      mask = network.buses.v_nom.isin(voltage_level)
      df = network.buses[mask]
  
      return df.index