docs: def _slice_idxs(df, twin=None):
      """
      Returns a slice of the incoming array filtered between
      the two times specified. Assumes the array is the same
      length as self.data. Acts in the time() and trace() functions.
      """
      if twin is None:
          return 0, df.shape[0]
  
      tme = df.index
  
      if twin[0] is None:
          st_idx = 0
      else:
          st_idx = (np.abs(tme - twin[0])).argmin()
      if twin[1] is None:
          en_idx = df.shape[0]
      else:
          en_idx = (np.abs(tme - twin[1])).argmin() + 1
      return st_idx, en_idx