docs: def buses_grid_linked(network, voltage_level):
      """ Get bus-ids of a given voltage level connected to the grid.
  
      Parameters
      ----------
      network : :class:`pypsa.Network
          Overall container of PyPSA
      voltage_level: list
  
      Returns
      -------
      list
          List containing bus-ids.
      """
  
      mask = ((network.buses.index.isin(network.lines.bus0) |
               (network.buses.index.isin(network.lines.bus1))) &
              (network.buses.v_nom.isin(voltage_level)))
  
      df = network.buses[mask]
  
      return df.index