Re: [ttml2] font*-p features

Any comments on this folks? I suggest there are a few different options
that would go along with removing the font*-p features:

   1. add informative note under each font* property with a font*-p feature
   that the specific listing of p was implied (but undocumented) in TTML1 (and
   perhaps should be added in TTML1 3ed);
   2. remove citation of p under application, but add a note like (1) anyway
   3. instead of using a note, add a special semantics subsection (or
   sub-sub-section if already present) that documents the semantics around p
   use of the font* property


On Sun, May 20, 2018 at 9:41 PM, Glenn Adams <glenn@skynav.com> wrote:

> I'm having second thoughts about adding the font*-p features in
> https://github.com/w3c/ttml2/pull/664/commits/
> 640f28ede06c0175e5d260af0790fef913e643ac.
>
> The reason we added these is because we explicitly added 'p' as one of the
> elements to which these font* properties applied. Now, why do they apply?
> Only for the purpose of determining the default line height for a paragraph
> (used to resolve 'normal'), since one has to resolve the font properties to
> a specific font resource (in order to obtain the ascent, descent, and line
> gap (separation) data from the font).
>
> But the thing is: all TTML1 implementations had to use this algorithm
> already, so effectively already applied these properties to 'p'. So in
> reality, we aren't adding new functionality here (that might warrant having
> new feature designators), but only rectifying a missing behavior
> specification (in TTML1) that was already implemented in reality (by both
> old implementations, like DFXPVW, and new implementations, like IMSCJS,
> which maps to CSS (which already applies these font properties to P in this
> fashion).
>
> I recommend we remove the new font*-p features and instead add notes to
> each of the properties that explains that the addition of 'p' to this list
> of applied elements serves only to document existing behavior consistent
> with TTML1 implementations.
>
> However, if someone knows of a TTML1 (or IMSC) implementation that does
> not use these semantics for obtaining the default line height of a
> paragraph, then we will need to discuss this further.
>
>