.ICS

Introduction

iCalendar is the standard text format for calendar data: events, to-do items and free or busy times. It was first published as RFC 2445 in 1998 and is now RFC 5545. Meeting invitations sent by email carry an .ics attachment, and calendar subscriptions, such as a sports fixture list or a public holiday feed, are .ics files fetched from a web address. It grew out of the older vCalendar format.

Structure

The file is UTF-8 text made of content lines, each NAME;PARAMETER=value:value, ending in a carriage return and line feed. Lines longer than 75 bytes are folded: the rest continues on the next line, which starts with a space.

Lines are grouped into components between BEGIN: and END: lines. The whole file is one VCALENDAR, which starts with VERSION:2.0 and a PRODID naming the program that made it. Inside are VEVENT, VTODO, VJOURNAL and VFREEBUSY components, VTIMEZONE definitions, and VALARM reminders nested in events. An event has a UID, a DTSTART, usually a DTEND or DURATION, a SUMMARY, and an optional RRULE for repeats.

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