Vertical Text

Writing Mode

Set writingMode="vertical-rl" on the <Text> component for vertical text. Characters flow top-to-bottom, columns progress right-to-left.

<Text font="NotoSansJP" fontSizePx={24} writingMode="vertical-rl">
  縦書きテキスト
</Text>

Character Orientation

• CJK characters — rendered upright (as-is)
• ASCII/Latin characters — rotated 90° clockwise (sideways)
• direction: ltr is fixed (RTL is not currently supported)

Vertical Layout

• Column width = lineHeightPx
• Column height = cumulative glyph advances; columns split when maxHeight is exceeded
• Columns are laid out right-to-left with lineHeightPx spacing
• OpenType vertical features (vert) are used for proper glyph substitution (e.g., punctuation positioning)

Fit in Vertical Mode

Vertical fit="shrink" and fit="grow" use the same fit contract as horizontal text:

• Fit condition: columns × lineHeightPx ≤ maxWidth AND max column height ≤ maxHeight
• Content and geometry that are both monotone-certified use binary refinement
• Negative tracking/proportional metrics and topology-changing flow exclusions use a descending exact grid bounded by fitMaxProbes
• The complete source is fitted before any ellipsis is applied
• fontSizePx and letterSpacingPx scale together; explicit lineHeightPx remains absolute

Rich Ellipsis in Vertical Mode

maxLines counts columns in vertical-rl. With ellipsis, plain text, Inline, Ruby, atomic InlineBox/InlineRect, and nested decoration use the same longest-legal-prefix planner as horizontal and exclusion-flow layout.

<Text
  font="NotoSansJP"
  fontSizePx={24}
  writingMode="vertical-rl"
  language="ja"
  wrap="char"
  maxLines={3}
  ellipsis
>
  縦組みの<Inline color="#0ea5e9">リッチ</Inline>文章は
  <Ruby>
    境界<Rt fontSizePx={10}>きょうかい</Rt>
  </Ruby>
  を保って最長の合法な接頭辞を表示します。
</Text>

The marker is synthetic and source-less. It inherits the first omitted effective text style and fragmentable decoration but is never placed inside an omitted ruby or atomic inline background.

Japanese Kinsoku (Line Breaking Rules)

Kinsoku (禁則) processing prevents typographically incorrect line breaks in Japanese text. Set language="ja" to enable it.

boundsvg uses a fixed JaTypesettingV1 profile informed by JLREQ and JIS X 4051. This is a deterministic release contract, not a claim of full JLREQ conformance.

Head-Prohibit Characters

Characters that must not appear at the start of a line:

、。，．・：；？！…‥
）］｝〕〉》」』】
〗〙゛゜‼⁇⁈⁉゠–—‐’”
｡､｣ﾞﾟ

Small kana, prolonged sound marks, wave dashes, and iteration marks are treated as JLREQ level-3 choice characters in JaTypesettingV1; they are allowed at line start by default.

ぁぃぅぇぉっゃゅょゎァィゥェォッャュョヮヵヶ
ー〜～々〻ゝゞヽヾ

Tail-Prohibit Characters

Characters that must not appear at the end of a line:

（［｛〔〈《「『【
〖〘‘“｢

Non-Breaking Pairs

• —— (consecutive em dashes) — never split
• …… (consecutive ellipsis leaders) — never split
• ‥‥ (consecutive two-dot leaders) — never split
• Consecutive ASCII digits are not split

Consecutive Kinsoku

When multiple head-prohibit characters appear consecutively (e.g., 」）。), they form a group that is moved together:

1. If a head-prohibit group would start a new line, pull the entire group back to the previous line
2. If it doesn't fit, backtrack up to 8 clusters to find a valid break point
3. If no valid break is found, use a forced break and report overflow.type = "kinsoku_unresolved" when the resulting plan remains physically contained

kinsoku_unresolved is diagnostic and does not trigger ellipsis by itself. If the plan also violates width, height, or maxLines, the physical overflow or cannot_fit status takes precedence.

Hanging Punctuation

Use hangingPunctuation to allow punctuation to extend beyond the text box boundary, producing flush text edges.

<Text
  font="NotoSansJP"
  fontSizePx={24}
  writingMode="vertical-rl"
  hangingPunctuation
>
  「日本語のテキスト」
</Text>

Known Limitations

• Mixed CJK + ASCII glyph positioning — In vertical-rl mode, when full-width Japanese and half-width ASCII/Latin characters are mixed, glyph visual positions may shift from the bounding box axis depending on font and renderer combinations. OpenType vertical features (vrt2/vert) and shaping offset normalization mitigate this, but the issue is not fully resolved.

• textOrientation — "mixed" and "upright" are supported. "sideways" is not yet implemented.

• TCY (tate-chu-yoko) — text-combine-upright is experimental and manual-only. The "all" value is accepted on <Inline> in vertical-rl mode; plain text digit runs are not grouped automatically.