縦中横 (tate-chū-yoko)

縦中横 (tate-chū-yoko, “horizontal in vertical”) is a typographic construct that lays a short run — usually digits, Latin letters, or mixed punctuation — horizontally inside otherwise vertical text. In print, it is the common treatment for two- or three-digit numbers in a vertical paragraph.

Notation

The annotation always uses the indirect-quoting form:

昭和27年生まれ［＃「27」は縦中横］

Renders as:

昭和<span class="aozora-tcy">27</span>年生まれ

The ［＃…］ directive looks back through the most recent text and applies the tcy treatment to the most recent occurrence of the quoted run. The target text is not re-emitted — the wrapper is applied in place, unlike bouten.

Container form

For longer mixed-orientation runs (multi-line table data, Latin abbreviations spanning a paragraph), the container form sits inside an outer indent block:

［＃ここから縦中横］
27 / 100 = 0.27
［＃ここで縦中横終わり］

Renders as:

<div class="aozora-tcy-block">
27 / 100 = 0.27
</div>

Common targets

(HTML escapes are handled by the renderer, not the AST.)

Anchor lookup

The lookup that finds the target run:

1. Scans backwards from the ［＃…］ directive through the current line.
2. Stops at the first match for the quoted run.
3. Falls through to the previous line if no match (with an upper bound of 64 KiB or one paragraph break, whichever comes first).

If no match is found, diagnostic aozora::lex::tcy_target_not_found fires and the directive degrades to a plain Annotation{Unknown}. Authors get the same look-back semantics they’d get from bouten — see Bouten for the symmetric case.

Why a span, not a flow rotation?

Web renderers reach for writing-mode: horizontal-tb inside a writing-mode: vertical-rl parent, but that has poor browser support and breaks line-break propagation. aozora’s HTML output uses a single class hook (<span class="aozora-tcy">) so the consuming stylesheet can decide:

• print stylesheet → font-feature-settings: "vert"; text-combine-upright: all;
• screen stylesheet → leave horizontal, set monospace
• e-book renderer → use the renderer’s native tcy primitive

Pushing this decision into the HTML output (e.g. emitting an inline SVG with rotated glyphs) would lock consumers into a specific typographic model. The class-hook output keeps the HTML semantic and defers presentation to the consumer.

AST shape

pub struct Tcy<'src> {
    pub text: &'src str,
    pub form: TcyForm,    // Inline | Container
    pub span: Span,
}

See also

• Indent containers — tcy commonly appears inside 字下げ blocks; the parser applies tcy after the indent fence is established so the look-back search is bounded by the inner block.