docs: def plot_tcoords(array, coords, scantypes=None, ax=None, **kwargs):
      """Plot coordinates related to the time axis.
  
      Args:
          array (xarray.DataArray): Array which the coodinate information is included.
          coords (list): Name of x axis and y axis.
          scantypes (list): Scantypes. If None, all scantypes are used.
          ax (matplotlib.axes): Axis you want to plot on.
          kwargs (optional): Plot options passed to ax.plot().
      """
      if ax is None:
          ax = plt.gca()
  
      if scantypes is None:
          ax.plot(array[coords[0]], array[coords[1]], label='ALL', **kwargs)
      else:
          for scantype in scantypes:
              ax.plot(array[coords[0]][array.scantype == scantype],
                      array[coords[1]][array.scantype == scantype], label=scantype, **kwargs)
      ax.set_xlabel(coords[0])
      ax.set_ylabel(coords[1])
      ax.set_title('{} vs {}'.format(coords[1], coords[0]))
      ax.legend()
  
      logger.info('{} vs {} has been plotted.'.format(coords[1], coords[0]))