iCalendar / jCal (RFC 5545, 7265)
This document defines the iCalendar data format for representing and exchanging calendaring and scheduling information such as events, to-dos, journal entries, and free/busy information, independent of any particular calendar service or protocol. [STANDARDS-TRACK]...
Also in the API standards catalog
This standard shows up on both sides of the house — as a data model here, and as a standard applied in API operations. Same standard, two lenses.
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