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[webvtt] comments from the CSS WG on WD-webvtt1-20141111

From: Bert Bos <bert@w3.org>
Date: Thu, 9 Apr 2015 11:21:22 +0200
To: public-tt@w3.org
Message-Id: <201504091121.31788.bert@w3.org>
The CSS WG looked at the first draft of webvtt and these are the comments we 
came up with:

1) The example in section 1.1 is possibly a use case for a new property and 
keyword for CSS, tentatively called 'text-wrap: balance', whose goals are to 
avoid that the last line of a paragraph is much shorter than the other 
lines. (The property appeared in an example in a WD once, but no definition 
has been published yet).

1a) Further investigation may be needed to see if and how this balancing 
(and the CSS property) applies to different scripts.

1b) And if the WebVTT use case and the CSS property are indeed the same 
feature, we'll need to see how precisely we want to define it: is it a good 
idea to specify a formula? (E.g., minimize a function that adds up a number 
of things like the total number of lines, the (absolute value or square of) 
each line's difference from the mean length, each line's difference from the 
available width, each line's difference from the previous line, each space's 
difference from the normal space width, the difference between the amount of 
stretching/shrinking in each line's spaces compared to the previous line, 
the difference in the amount of letter spacing in each line compared to the 
previous line, the occurrences of "rivers", etc.); or is it better to just 
give hints about possible factors to take into account and leave room for 
implementations to do better (but slower) or worse (but faster)?

2) Section 5.5: Some people wonder if HTMLElement is the right type to use 
for all the nodes, or if it is better to use more specific subclasses.

3) The list in that section doesn't match with the description of how 
Selectors work; in particularly, Class, Voice, and Lang objects are all 
"span" elements here, but are "c", "v", and "lang" elements in Selectors. 
Selectors is written on top of the DOM, though, so these should match. (But 
we hear this difference is intentional?)

4) Related to the previous, this section doesn't seem to apply the IDs of 
region objects.

5) Section 6.2.3.1: "group of selectors" has no defined meaning. You 
probably want either "compound selector list" or "complex selector list".

6) You can remove the entire section about how to evaluate the selector
once section 5.5 defines an accurate DOM mapping; just specify that it
matches over the equivalent DOM defined in 5.5. Or are there (intentional) 
differences between selecting against a WebVTT DOM and the mapped HTML DOM?

7) Section 6.2.3.3: It looks like cue regions are basically blocks that get
filled with cues. Why not just make those an element selectable by ::cue()?
You're limited to the same styles that apply to ::cue anyway.

8) Even though regions have an ID, it looks like you can't select by
it. All you can do is apply styles to all regions. What's the
purpose of this, then? It seems equivalent to ::cue with no argument,
except maybe the background property would apply over a wider box.

9) Regarding external stylesheets, several people recommend against trying 
to use sheets from the outer document (except for style rules that use 
::cue()). Can WebVTT be extended to ref an external stylesheet?



For the CSS WG,
Bert
-- 
  Bert Bos                                ( W 3 C ) http://www.w3.org/
  http://www.w3.org/people/bos                               W3C/ERCIM
  bert@w3.org                             2004 Rt des Lucioles / BP 93
  +33 (0)4 92 38 76 92            06902 Sophia Antipolis Cedex, France

Received on Thursday, 9 April 2015 09:21:41 UTC

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