vcalendar

VCALENDAR is the top-level component of the iCalendar data format, used to represent and exchange calendaring information. It is defined in RFC 5545 (with historical precedence from RFC 2445) and is widely used by calendar applications and servers to share events, tasks, and availability data.

A VCALENDAR object is a text representation that begins with BEGIN:VCALENDAR and ends with END:VCALENDAR. It contains calendar-wide properties and one or more calendar components, such as VEVENT (events), VTODO (to-dos), VJOURNAL (notes), and VFREEBUSY (free/busy information). Each component is enclosed by BEGIN:COMPONENT and END:COMPONENT.

Core properties include VERSION (typically 2.0) and PRODID (an identifier for the producing software). Optional properties include CALSCALE (usually GREGORIAN) and METHOD (used when transporting changes via iTIP, for example PUBLISH or REQUEST).

Time zones are defined using VTIMEZONE components; events may specify DTSTART and DTEND with a UTC time, a local time, or a TZID parameter referencing a VTIMEZONE. Recurring events use RRULE and related properties to describe repetition, supported by RDATE and EXDATE as needed.

Serialization uses ASCII text with lines folded at 75 octets, and long lines continued on the next line with a leading space or tab, ensuring compatibility across systems.

VCALENDAR is central to exchange mechanisms such as CalDAV and iCalendar subscriptions. It is supported by major calendar software for import/export, synchronization, and collaborative scheduling.