Upright text in vertical lines doesn't segment correctly

[r12a]

This issue is applicable to many Indian languages.

When upright characters appear in vertical lines of text, browsers need to tailor grapheme cluster rules so that full orthographic syllables represented as conjuncts, are kept together.

See requirements at: Indic Layout Requirements, but add to those the points made in Typographic character units in complex scripts.

The GAP

Gecko appears to segment on grapheme clusters. Blink, and Webkit keep conjuncts together. But all engines have problems with vowel-signs, especially but not only pre-base vowel-signs.

Priority

Marked as advanced, since vertical text is not a common use case. In writing sytems like modern Tamil, it is even less common, since conjuncts are rarely used.

Tests

Interactive test, When devanagari characters are rendered upright in vertical text, orthographic syllables containing conjuncts are kept together

Action taken

Gecko • Blink • Webkit

Outcomes

tbd

[r12a]

The first comment in this issue contains text that will automatically appear in the various Indic gap-analysis documents, in the Vertical Text section, as a topic with the same title as this issue. Any edits made to that comment will be immediately available in the document. Proposals for changes or discussion of the content can be made in comments below this point.

[xfq]

Updated the link to Typographic character units in complex scripts and added links to browser bug reports.