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[webvtt] 3.1 Line wrapping for non-Latin scripts [I18N-ISSUE-434]

From: Phillips, Addison <addison@lab126.com>
Date: Fri, 20 Mar 2015 20:49:35 +0000
To: "public-tt@w3.org" <public-tt@w3.org>
CC: "public-i18n-core@w3.org" <public-i18n-core@w3.org>
Message-ID: <7C0AF84C6D560544A17DDDEB68A9DFB52ECB5D94@ex10-mbx-9007.ant.amazon.com>
I18N comment: https://www.w3.org/International/track/issues/434


3.1 Text track cues
http://www.w3.org/TR/2014/WD-webvtt1-20141111/#text-track-cues


Line wrapping should take into account the special rules needed for scripts such as the following:

- Chinese, Japanese and Korean wrap after characters, but don't put certain characters at the start/end of a line

- Thai and other SE Asian scripts wrap at word boundaries, but words are not delimited by spaces – spaces are instead used to separate phrases.

- Tibetan wraps after the tsek character that follows a syllable – words are not separated by spaces.

- Indic and other complex scripts break at orthographic syllable boundaries, which are often two or more grapheme clusters.

See http://www.w3.org/TR/css3-text/#line-breaking for additional background. (http://r12a.github.io/scripts/tutorial/part5 provides additional examples, if needed.)

6.2.1 says that "Text runs must be wrapped according to the CSS line-wrapping rules", but that is a little vague (and, to be honest, the CSS information on script behaviour is also somewhat sparse). No mention is made of default settings for the line-break and word-break properties.

It would be good, as a minimum, to remind implementers that script-specific wrapping algorithms need to be supported for WebVTT content.

(6.2.2 says that "the 'word-wrap' property must be set to 'break-word'". Note that a alternative, and somewhat more descriptive name for this property is overflow-wrap.)

In addition, we noticed in:

http://www.w3.org/TR/webvtt1/#cues-with-multiple-lines 

In Section 1.1, there is discussion about line-wrapping and line-breaking. The examples are given in English. "Balancing" line wrapping might take different forms because of the presentational needs of various langauges.

Received on Friday, 20 March 2015 20:50:00 UTC

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