[webvtt] 6.2.1 processing model handling of bidi [I18N-ISSUE-432]

I18N comment: https://www.w3.org/International/track/issues/432

6.2.1 Processing model

In section 6.2.1 I find the instruction quoted below. This seems to be trying to determine the base direction, but I don't see other elements of implementing BIDI elsewhere in processing, such as using 'direction' to set the meaning of 'start' and 'end' and I don't see any discussion of handling directional runs in presentation (is that on a different level??)

Apply the Unicode Bidirectional Algorithm's Paragraph Level steps to the concatenation of the values of each WebVTT Text Object in nodes, in a pre-order, depth-first traversal, excluding WebVTT Ruby Text Objects and their descendants, to determine the paragraph embedding level of the first Unicode paragraph of the cue. [BIDI]

Within a cue, paragraph boundaries are only denoted by Type B characters, such as U+000A LINE FEED (LF), U+0085 NEXT LINE (NEL), and U+2029 PARAGRAPH SEPARATOR. (This means each line of the cue is reordered as if it was a separate paragraph.)

If the paragraph embedding level determined in the previous step is even (the paragraph direction is left-to-right), let direction be 'ltr', otherwise, let it be 'rtl'.

It would be helpful to the author to be able to set the default base direction for a whole WebVTT file to rtl.

It would also be helpful if the author could set the base direction for each cue explicitly, since the Unicode paragraph detection algorithm can be fooled by a paragraph that starts with a strong LTR character, but is actually a RTL paragraph (or vice versa), eg. "نشاط التدويل is how you say 'i18n Activity' in Arabic."

Received on Friday, 20 March 2015 20:46:34 UTC