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2. Conventions and Terminology

2.1 Requirement keywords

The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in BCP 14 (RFC 2119, RFC 8174) when, and only when, they appear in all capitals, as shown here.

2.2 Grammar notation

Grammar is given in ABNF (RFC 5234), with terminals expressed as Unicode scalar values (%xNNNN). The collected grammar is Annex D; fragments are inlined where relevant. Because notation is embedded in free Japanese text, the grammar's text production is disambiguated from constructs by the leftmost-longest rule of §5, not by ABNF negation.

2.3 Definitions

  • Source — the input byte sequence (§3), decoded to Unicode scalar values.
  • Sanitized source — the source after the §4 normalization pass. Unless stated otherwise, all byte offsets in this document and in conformance vectors are UTF-8 byte offsets into the sanitized source. For input with no BOM, no CR, and no 〔…〕 accent span, the sanitized bytes equal the source bytes.
  • Directive — a bracketed annotation ［＃ … ］ (§5, §6). The text between ＃ and ］ is the directive's body.
  • Inline construct — a notation that attaches within a line: ruby, bouten/bousen, tate-chu-yoko, gaiji, kaeriten, warichu, and the generic annotation.
  • Container — a construct delimited by a paired opener and closer that governs the enclosed content (§7): block layout (字下げ etc.), 罫囲み, and the inline 傍点/傍線 range and 割り注.
  • Ruby — a reading (furigana) attached to a base run, ｜base《reading》 or its implicit form (§6.1).
  • Gaiji (外字) — a character outside the assumed repertoire, written as a ※［＃…］ reference resolved to a Unicode scalar where possible (§6.4).
  • Men-ku-ten (面区点) — a JIS X 0213 plane-row-cell address, e.g. 第3水準1-85-54, used to identify a gaiji (§6.4, Annex B).
  • Kunten / kaeriten (訓点・返り点) — classical-Chinese reading marks (§6.5).
  • Processor — any implementation that consumes the notation. A conforming processor satisfies §10.
  • Diagnostic — a structured, non-fatal observation a processor reports about the input (§9). Processing always continues and produces a best-effort result.

2.4 Error-handling philosophy

The notation has no concept of a fatal parse error. A conforming processor MUST always produce a result for any input, however malformed, and MUST NOT abort. Malformed or suspect input is surfaced through the diagnostics of §9 while the affected construct degrades to a defined best-effort form (typically the literal text, or a generic annotation that preserves the bytes). This recoverability requirement is what lets the same processor handle a century of hand-entered files.

2.5 Character repertoire and code points

Significant full-width delimiters are referred to by their Japanese glyph and Unicode scalar value; the canonical list is in Annex D. The most important are ［=U+FF3B, ＃=U+FF03, ］=U+FF3D, 《=U+300A, 》=U+300B, ｜=U+FF5C, ※=U+203B, 「=U+300C, 」=U+300D, 〔=U+3014, 〕=U+3015.