6.10 Headings (見出し)

Synopsis

A heading marks a run of text as a structural title. Aozora distinguishes three levels (大 / 中 / 小見出し) and, orthogonally, three styles — standard, same-line (同行, the title shares its line with the body that follows) and window (窓, an inset title). Style and level combine freely: 同行中見出し, 窓小見出し, and so on. Headings are most often expressed as a forward-reference hint that promotes or marks a quoted run.

Notation

A heading is written in one of three forms — a forward-reference hint, a paired delimiter, or a block (ここから…) delimiter:

　　　　序［＃「序」は大見出し］                           ← hint (forward-reference)
萩原朔太郎［＃「萩原朔太郎」は同行中見出し］　二十年の友。…  ← hint (same-line)
［＃窓小見出し］チベット探検の動機［＃窓小見出し終わり］     ← paired
［＃ここから中見出し］本文…［＃ここで中見出し終わり］       ← block

heading-hint         = LBRACK HASH LQUOTE target RQUOTE %s"は" [ style ] level %s"見出し" RBRACK
heading-paired-open  = LBRACK HASH [ style ] level %s"見出し" RBRACK
heading-paired-close = LBRACK HASH [ style ] level %s"見出し終わり" RBRACK
heading-block-open   = LBRACK HASH %s"ここから" [ style ] level %s"見出し" RBRACK
heading-block-close  = LBRACK HASH %s"ここで" [ style ] level %s"見出し終わり" RBRACK
level                = %s"大" / %s"中" / %s"小"
style                = %s"同行" / %s"窓"

The optional style prefix selects 同行 (same-line) or 窓 (window); its absence is the standard style. Style and level pair freely (…は同行中見出し, ［＃窓小見出し］, ［＃ここから大見出し］). The 窓 style appears almost exclusively in the paired form.

Parameters

target — (hint form) the quoted run promoted or marked as a heading (resolved by §7.5). The paired and block forms have no quoted target: the content delimited between the opener and closer is the heading text.
level — 大 / 中 / 小.
style — standard (no prefix), 同行 (same-line), or 窓 (window).

Semantics

A heading hint resolves its target (§7.5) and carries the level and style. It promotes that run to a heading node when the target is the bare line immediately preceding the directive — the run is pulled out of the flow and becomes the heading. When the referent is not such a clean preceding line, the hint is retained inline (a heading-hint marker) rather than promoted, so no run is mis-titled and no input is lost. The quoted target is matched ruby-stripped (§7.5), so a title carrying ruby — 両頭《りやうとう》の蛇《へび》 — is still recognised by its base text 両頭の蛇 (retained as a hint, since a ruby-bearing run is not a clean bare line). The 同行 (same-line) and 窓 styles in practice run into the body on their own line, so they are typically retained as hints; the standard style with a bare title line is the usual promotion case.
A paired (［＃<style?><level>見出し］ … ［＃<style?><level>見出し終わり］) or block (［＃ここから…見出し］ … ［＃ここで…見出し終わり］) opener/closer pair (§7.1) delimits its content explicitly and yields a heading node wrapping that content — no forward reference or promotion is involved. Pairing is by the heading family at a matching level and style; a closer of a different level or style than its opener is a mismatch (§7.2). The 窓 style uses the paired form almost exclusively; the standard and 同行 styles occur in all three forms.
Reference rendering (§8): a promoted standard 大 / 中 / 小 heading is <h1>–<h3> (class="aozora-heading aozora-heading-<large|medium|small>"); the 同行 / 窓 styles add an aozora-heading-<same-line|window> modifier (and 窓 renders as a styled <div> rather than an outline <hN>); a referent-present unpromoted hint is a hidden inline marker (<span class="aozora-heading-hint" data-level=… data-style=… data-target=… hidden>), with data-style present only for a non-standard style, while a self-contained hint (see Error conditions) renders its target visibly (<span class="aozora-heading-hint" data-level=…>X</span>, no hidden, no data-target) — the inline analogue of a heading, valid where the directive sits mid-line. The precise tag is part of the reference mapping (§8.2), not mandated. The paired and block forms render the same heading element (<hN> / <div> with the level and style classes) wrapping their delimited content directly (phrasing content, not a nested paragraph).
Serialization reconstructs the directive (the hint's literal target, or the paired / block opener and closer around the content) byte-exact (§7.6).

Error conditions

A single-target heading hint whose target is absent from the look-back is not an error: it is a self-contained forward heading — the quoted run is itself the heading text, retained as a visible heading-hint marker (never promoted, since there is no preceding line to reclaim). §6.14 degradation does not apply, as with the other forward references (§6.2, §6.12, §7.5).
A multi-quote heading hint with any missing referent still degrades to a generic annotation (§6.14): a non-contiguous referent cannot be spliced into a single heading run.

Conformance vectors

heading, heading_hint, heading_forward_no_referent, heading_ruby_hint, heading_promoted, heading_same_line, heading_window, heading_paired_window, heading_block.

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