BEGINVTIMEZONE

BEGINVTIMEZONE is a property name used in the iCalendar data format to mark the start of a VTIMEZONE component. The iCalendar specification (RFC 5545) defines VTIMEZONE as a container that supplies the definition of a time zone, including its standard and daylight saving time rules. By enclosing the component between BEGIN:VTIMEZONE and END:VTIMEZONE, calendar applications can interpret date‑time values correctly across different geographic regions.

A VTIMEZONE component typically contains one or more subcomponents: a TZID property that identifies the time zone, a LAST‑MODIFIED property indicating the most recent update, and one or more observance subcomponents such as STANDARD and DAYLIGHT. Each observance defines the offset from Coordinated Universal Time (UTC), the effective start date, and recurrence rules that describe transitions between standard time and daylight‑saving time.

The BEGINVTIMEZONE line is therefore essential for interoperability. When an iCalendar object includes date‑time values that are not expressed in UTC, the accompanying VTIMEZONE allows receiving applications to convert those values to the local time zone of the user. If a VTIMEZONE is omitted, the calendar data may fall back to default time‑zone assumptions, potentially leading to incorrect event times.

Implementations of iCalendar parsers must recognize the BEGINVTIMEZONE and ENDVTIMEZONE delimiters, parse the enclosed properties, and apply the defined offsets when rendering events. Compatibility across platforms such as Microsoft Outlook, Google Calendar, and Apple Calendar depends on the consistent handling of these components.