code: func (t *TimeOfDay) Validate(c *validation.Context) {
  	if t.GetDay() == dayofweek.DayOfWeek_DAY_OF_WEEK_UNSPECIFIED {
  		c.Errorf("day must be specified")
  	}
  	_, err := t.toTime()
  	if err != nil {
  		c.Errorf("%s", err)
  	}
  }
docs: // Validate validates this time of day.