Page & section breaks (改ページ・改丁)

Aozora Bunko inherits print conventions for page-level structure. Four annotations split a work into pages, signatures, and openings:

All four are self-contained directives — no opener / closer pair, no inner content. They appear on their own line in the source.

AST shape

［＃改ページ］ is its own borrowed-AST node; the three 段 / 丁 / 見開き breaks share one SectionBreak node tagged by [SectionKind]:

// borrowed::AozoraNode variants
AozoraNode::PageBreak,                  // ［＃改ページ］
AozoraNode::SectionBreak(SectionKind),  // ［＃改丁 / 改段 / 改見開き］

pub enum SectionKind {
    Choho,   // 改丁
    Dan,     // 改段
    Spread,  // 改見開き
}

Why distinct variants for each break flavour?

The flavours render to identical HTML structure (an empty <div>) but different class hooks (aozora-page-break, aozora-section-break-{kaicho,kaidan,kaimihiraki}). Keeping PageBreak separate and tagging the section flavours with a SectionKind enum (rather than a string) means:

• The renderer never plumbs the original notation through to the output, preserving the AST’s role as a normalised IR.
• The compiler’s exhaustiveness check guarantees every flavour has a render path.
• Tooling can count breaks of a specific flavour at the AST level without a string match.

Composition with other annotations

Breaks unconditionally close any open inline annotation (ruby, bouten, tcy) at their line. They do not close container directives (字下げ, 地付き, etc.) — those persist across page boundaries, which matches print typography.

［＃ここから2字下げ］
　第一節
［＃改ページ］
　第二節 (still 2字下げ)
［＃ここで字下げ終わり］

Diagnostics

See also

• Indent containers — containers persist across breaks.