[BCP 14] S. Bradner, Key words for use in RFCs to Indicate Requirement
Levels, RFC 2119, March 1997; and
B. Leiba, Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words,
RFC 8174, May 2017.
[RFC 5234] D. Crocker, Ed., P. Overell, Augmented BNF for Syntax
Specifications: ABNF, RFC 5234,
January 2008.
[RFC 7405] P. Kyzivat, Case-Sensitive String Support in ABNF,
RFC 7405, December 2014.
[JISX0213] JIS X 0213, 7-bit and 8-bit double byte coded extended
Kanji sets for information interchange. Used for gaiji men-ku-ten
addressing (§6.4, Annex B).
[AOZORA-ANNOTATION] Aozora Bunko, 注記一覧 (annotation guide).
https://www.aozora.gr.jp/annotation/. The authoritative human-facing
description this specification formalises (§1.2). Snapshot date is recorded
per citing section / decision record.