Returns whether the given date and timezone are in daylight saving time.
isInDaylightSavingTime( date, timezone )
date: (Date) The date in which the expression should evaluate.
timezone: (Text) The string Id of a timezone.
Boolean
You can copy and paste these examples into the Expression Rule Designer to see how this works.
isInDaylightSavingTime(date(2005,12,13),"America/Los_Angeles")
returns false