Definition of "text alignment" doesn't match processing requirements

[zcorpan]

https://w3c.github.io/webvtt/#webvtt-cue-text-alignment

A text alignment
An alignment for all lines of text within the cue box, in the dimension of the writing direction and the paragraph direction [BIDI], one of:

Start alignment
The text is aligned towards the paragraph direction start side of the cue box.

As far as I can tell, this text is wrong. The processing model sets 'unicode-bidi' to plaintext which isolates paragraphs, and then sets 'text-align' to start for "Start alignment", and the behavior of CSS in that case does not match the description above.

See
http://software.hixie.ch/utilities/js/live-dom-viewer/saved/3719
and flip the value of 'text-align' between start and end (in Gecko or WebKit or Blink), to see what the effect of the processing requirements are.

So for start alignment, each line is aligned to the start edge for that line, which is separate from the cue's "paragraph direction".

My understanding is that @r12a is happy with the effect of the processing requirements, so I suggest we fix the description here to match.

[silviapfeiffer]

WFM.

[zcorpan]

So when this is fixed, I cannot find anything that actually uses the "paragraph direction", since the position alignment now doesn't do anything differently depending on "paragraph direction" (previously, a start-aligned cue with RTL first paragraph would have position alignment be right, but currently it's left (in horizontal)).

There are no CSS properties that apply to ::cue that change behavior depending on what 'direction' is set to, either. (e.g. 'padding-start' would be something that depends on 'direction'.)

Unless I'm missing something, this means that we can drop the "paragraph direction" concept entirely.