TZOFFSETTO0400

TZOFFSETTO0400 is a reference to a component used in iCalendar data (ICS) to define time zone transitions. Specifically, TZOFFSETTO is a parameter within a VTIMEZONE component that indicates the UTC offset after a given transition, such as when moving from standard time to daylight saving time or vice versa. The value is a signed four-digit offset in HHMM from UTC.

In correct ICS syntax, TZOFFSETTO is written with a leading sign, for example TZOFFSETTO:+0400 or TZOFFSETTO:-0500. The sign and the HHMM portion specify the new offset that should be applied after the transition. TZOFFSETFROM is typically paired with TZOFFSETTO to describe the offset before the transition, providing a complete picture of the change in local time.

TZOFFSETTO is used together with a DTSTART (the moment of the transition), and often with RRULE or BYMONTH/BYDAY rules to describe recurring transitions. These components together allow calendar applications to convert local times to UTC and back, accounting for daylight saving rules and historical changes.

Common usage context

- In ICS files, a VTIMEZONE component contains STANDARD and/or DAYLIGHT subcomponents, each including TZOFFSETFROM and TZOFFSETTO values.

- Applications such as calendar clients rely on these lines to compute local time for events across different time zones and years.

Notes

- The explicit sign is required; a form like TZOFFSETTO0400 without a sign is not valid ICS syntax.

- The actual offset represented by TZOFFSETTO depends on the time zone's defined rules; +0400 indicates a UTC offset of plus four hours.