docs: def validate_err_calc(val):
      """Validation function for the
      :attr:`psy_simple.plotter.FldmeanPlotter.err_calc` formatoption"""
      try:
          val = validate_float(val)
      except (ValueError, TypeError):
          pass
      else:
          if val <= 100 and val >= 0:
              return val
          raise ValueError("Percentiles for the error calculation must lie "
                           "between 0 and 100, not %s" % val)
      try:
          val = ValidateList(float, 2)(val)
      except (ValueError, TypeError):
          pass
      else:
          if all((v <= 100 and v >= 0) for v in val):
              return val
          raise ValueError("Percentiles for the error calculation must lie "
                           "between 0 and 100, not %s" % val)
      try:
          val = validate_str(val)
      except ValueError:
          pass
      else:
          if 'std' not in val:
              raise ValueError(
                  'A string for the error calculation must contain std!')
      return val