[1] RFC 5070 - The Incident Object Description Exchange Format (2017-05-07 20:04:30 +09:00) https://tools.ietf.org/html/rfc5070#section-2.9

[2] RFC 7970 - The Incident Object Description Exchange Format Version 2 (2017-05-14 16:49:04 +09:00) https://tools.ietf.org/html/rfc7970#section-2.8