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

pub enum Break {
    Page,
    PageRecto,        // 改丁
    PageSpread,       // 改見開き
    Section,          // 改段
}

pub struct BreakNode {
    pub kind: Break,
    pub span: Span,
}

Why distinct variants for each break flavour?

The four flavours render to identical HTML structure (an empty <div>) but different class hooks. Collapsing them to a single variant with a string tag would:

• Force the renderer to plumb the original notation through to the output, defeating the AST’s role as a normalised IR.
• Lose the type-system check that every break flavour has a render path — clippy’s exhaustiveness lint catches the bug at compile time.
• Make it impossible to count page breaks of a specific flavour at the AST level without a string match.

The 4-variant enum is 1 byte plus discriminant — no real cost over the alternative.

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.