1897472 - Line breaking doesn't conform to Unicode 15.1

Status: NEW

(Core :: Internationalization, defect)

Description

[Norbert Lindenberg]

With Unicode 15.1, the Unicode line breaking algorithm specified in UAX 14 was updated to support line breaking at orthographic syllable boundaries. Such line breaking is required for a number of Brahmic scripts, including Javanese, Balinese, Brahmi, and more.

Firefox 126 doesn't conform to this updated standard yet. The problem can be seen at
https://lontar.eu/unicode/line-break/balinese.html

The first framed text box on that page is the test case. The second framed text box uses zero width space characters to show what the first box should look like: Text should stay within the box, and line breaks should occur at orthographic syllable boundaries near the right border. Actual behavior in Firefox 126, however, is that line breaks only occur at punctuation, and that several long lines run out of the box.

For the current specification, see:
https://www.unicode.org/reports/tr14/

For background on the change, see the proposal:
https://www.unicode.org/L2/L2022/22080r2-line-break-ortho-bnd.pdf

Note that the updated specification is supported in ICU 74, and that Safari has already been updated to provide correct line breaking at orthographic syllable boundaries.

Comment 1

[Ting-Yu Lin [:TYLin] (PDT, UTC-7)]

Thanks for the bug report. Firefox's line breaking algorithm is depending on ICU4X line segmenter, and we are aware that it is not yet conform to the Unicode 15.1. The work is tracked in https://github.com/unicode-org/icu4x/issues/3255

Comment 2

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:m_kato, could you have a look please?

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