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[[ 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] ]] http://dev.w3.org/html5/webvtt/#webvtt-cue-text-rendering-rules As far as I can tell, the paragraph separators for the purpose of the referenced step P1 are class B characters only. It would be nice to call it out explicitly. TR9 talks about "appropriate Newline Function" which, per 5.8 Newline Guidelines in Unicode, is platform-dependent but the listed examples are all class B characters. TR9 also talks about "higher-level protocol paragraph determination" but WebVTT doesn't have those, I think. Hence, the paragraph separators are the class B characters.
Certainly it can be clarified...
Checked in as WHATWG revision r7428. Check-in comment: Clarify how bidi paragraph separation works http://html5.org/tools/web-apps-tracker?from=7427&to=7428