def CheckValidText(self, diagnostics, time_field, cron_time_field):
    if time_field.lower() not in cron_time_field.valid_text:
      diagnostics.append('%s is not valid for field "%s" (%s)'
                         % (time_field, cron_time_field.name, self))
Checks if a field has valid text.
dataset/ETHPy150Open lyda/chkcrontab/chkcrontab_lib.py/CronTimeField.CheckValidText