[ttml2] Action-369 - collate smpte issues and draft dispositions

As per action-369, here is my first pass at the SMPTE issues and our draft dispositions for them, for review:

NB the dispositions are intended to capture the sense of the implementation state, with the intent that if that is captured correctly it should be edited as needed prior to issuing as a formal communication.

Guidance is requested on two issues, highlighted in red.

Relating to the liaison at https://lists.w3.org/Archives/Member/w3c-archive/2012Sep/0214.html – I considered the previous requests concerning metadata to be out of scope of this action.

tts:disparity
This is Issue-224

Disposition: Implementing using the tts:disparity style attribute applicable to div, p and region, as a positive or negative length value matching the requested semantics. Note that the animate element may be used to continuously animate the value of this style attribute if required.


tts:fontSize as percentage of root container dimensions
This is Issue-225 - CLOSED

Disposition: Implemented by adding vw and vh metrics to all values whose syntax is specified as <length>, where vw is 1% of the width of the root container region and vh is 1% of the height of the root container region.


<p> origin and extent
This is Issue-226 – CLOSED duplicate of Issue-176 – CLOSED.

Disposition: Implemented by permitting tts:origin and tts:extent to be specified on <p> and <div> as a shorthand for specifying an inline region.


<p> fade-up and –down
- apply tts:opacity to <p>
This is Issue-227 - CLOSED

Disposition: Implemented: tts:opacity style attribute now applies to body, div, p, region and span, and the animate element may be applied for specifying continuous (as opposed to discrete) changes to styling attributes including opacity.


Ruby text
- position before or after
- offset –1.0 em to +infinity
This is Issue-228 - CLOSED

Disposition: Implemented within constraints of Ruby Annotations http://www.w3.org/TR/2001/REC-ruby-20010531/#abstract-def using new syntax, i.e. by introducing ruby attributes on <span> elements, not by introducing <ruby>, <rt>, <rb> etc elements as per HTML5.

GUIDANCE REQUIRED: has the request been fully or only partially met by the solution?


Mixed vertical-horizontal progression direction
This is Issue-357 – CLOSED duplicate of Issue-229 – CLOSED.

Disposition: Implemented using tts:textCombine style attribute based on semantics on CSS Writing Modes §9.1. This allows horizontal text in a <span> to be inserted into vertical writing mode text so that the combined glyph areas fit in the em square of the surrounding vertical text. If the desired effect is to extend beyond a single em square, the applicable font size in the surround area can be increased to make the em square bigger in the context of the horizontal group.

GUIDANCE REQUIRED: does this solution also require use of tts:textOrientation?


Forced display
This is Issue-230 - CLOSED

Disposition: Implemented using the condition attribute and a bound parameter named 'forced' - this allows the value of for example the style attribute tts:visibility to be conditionally set to "visible" or "hidden" on style elements which can then be applied to the text that is 'non-forced' to determine whether or not it should be rendered.


Individual character rotation
This is Issue-229 - CLOSED

Disposition: Implemented using the tts:textOrientation style attribute that can be applied to a <span>.


Bottom-to-top text direction
This is Issue-232 - CLOSED

Disposition: Not implemented – marked as 'won't fix'. We have not identified a use case for this. If there is a use case please tell us what it is. Also note that there is no support for bottom to top writing mode in CSS so a mapping into HTML/CSS may not be possible for this feature.


Superscript and subscript character style
- baseline vertically offset by –0.5em or +0.5em
- fontsize 0.6em

This is Issue-233 – CLOSED duplicate of Issue-24 – CLOSED.

Disposition: Implemented using the tts:fontVariantPosition style attribute with values normal/sub/super and semantics based on CSS Fonts §6.5. Note that the requested behaviour of baselines offset by +0.5em or –0.5em and a font size of 0.6em is not required by this solution, but may be acceptable in some implementations. However it would be preferable to avoid offsetting the baseline and use the superscript and subscript variant glyphs in the font where available, or where not available, to use the subscript and superscript fallback metrics specified within the font t's OS/2 table. fontVariationPosition does apply cumulatively to nested <span>s.


Drop shadow character style
- diagonally below and to the right
- specify color
- specify thickness in em

This is Issue-234 - CLOSED
Disposition: Implemented using the tts:textShadow style attribute, based on the semantics of CSS Text Decoration Module Level 3 §4 text-shadow property.


Feathering of shadow and outline effects

This is Issue-235 - CLOSED
Disposition:  Implemented using the tts:textShadow style attribute, based on the semantics of CSS Text Decoration Module Level 3 §4 text-shadow property.


Character spacing, i.e. Letter-spacing with a span in units of em from –1em to +infinity
Inline space –1em to +infinity

This is Issue-236 duplicated as Issue-354 - CLOSED
Disposition: Implemented using the tts:letterSpacing style attribute, based on the semantics of CSS Text Module Level 3 §8.2 letter-spacing property.

[end of requests]