@Pattern(regexp = "(?i)(NANOSECONDS|MICROSECONDS|MILLISECONDS|SECONDS|MINUTES|HOURS|DAYS)",
			message = "timeUnit must be one of NANOSECONDS, MICROSECONDS, MILLISECONDS, SECONDS, MINUTES, HOURS, DAYS (case-insensitive)")
	public String getTimeUnit() {
		return timeUnit;
	}
Mixin for options that include a periodic fixed-delay trigger.
fixedDelay remains in annotated classes to avoid breaking changes
due to differing defaults.

@author Gary Russell
spring-xd-module-spi/src/main/java/org/springframework/xd/module/options/mixins/PeriodicTriggerMixin.java