{minutes} TTWG Meeting 2018-05-31

Thanks all for attending today's TTWG meeting. Minutes can be found in HTML format at https://www.w3.org/2018/05/31-tt-minutes.html


In text format:


   [1]W3C

      [1] http://www.w3.org/


                Timed Text Working Group Teleconference

31 May 2018

   See also: [2]IRC log

      [2] https://www.w3.org/2018/05/31-tt-irc


Attendees

   Present
          Nigel, Glenn, Cyril

   Regrets
          Pierre, Andreas, Thierry

   Chair
          Nigel

   Scribe
          nigel

Contents

     * [3]Topics
         1. [4]This Meeting
         2. [5]TTWG Charter
         3. [6]Clean up and refactor features (#688, #763, #789,
            #790, #791, #792, #… ttml2#794
         4. [7]Add features for standard and high dynamic range
            PNG images (#694, #6… ttml2#770
         5. [8]Remove @style from animate and set (#703).
            ttml2#707
         6. [9]Describe generically compliant processors that
            support only external … ttml2#755
         7. [10]Exclude vertical length offset as 1st component in
            2 component positi… ttml2#769
         8. [11]Add explicit exceptions to ignoring element
            semantics with condition … ttml2#772
         9. [12]Clarify distinction between validation processing,
            validation process… ttml2#777
        10. [13]Collapse language for style application to
            paragraph text nodes; add … ttml2#803
        11. [14]Add xml:base to core vocabulary (#804). ttml2#808
        12. [15]Add #unicodeBidi-version-2 feature designator
            (#679). ttml2#759
        13. [16]Add and update element derivations (#380).
            ttml2#805
        14. [17]CR2 issues with no pr open label on them
        15. [18]Time containment semantics for smpte time base.
            ttml2#377
        16. [19]Negative feature designators aren't future proof.
            ttml2#697
        17. [20]tts:rubyReserve length component semantics
            ttml2#779
        18. [21]Use of maximum descendant font size in normal line
            height computation. ttml2#806
        19. [22]Meeting close
     * [23]Summary of Action Items
     * [24]Summary of Resolutions
     __________________________________________________________

   <scribe> scribe: nigel

This Meeting

   Glenn: The main thing I want to do today is review #794 with a
   view to merging early.

   Nigel: Today we have some regrets, so let's make what progress
   we can.
   ... On the agenda is TTWG Charter, TTML2, and I'm not sure what
   else we can cover.
   ... Aside from #794 is there anything else you'd like to make
   sure we look at, or any other
   ... business?

   Glenn: #770.

   Nigel: OK

   Glenn: In the remainder of the time I'd like to go over the
   ones ready to go pending
   ... approval of recent updates to address comments, that are
   marked as pending re-review
   ... in the pull request list for TTML2. There are a couple of
   older ones with Nigel's name on
   ... that maybe we can do in realtime.

   Nigel: OK

   Glenn: #703 and #755 I think.

   Cyril: Nothing more from me.

TTWG Charter

   Nigel: Just to note for the minutes we are now operating under
   a new Charter:

   [25]TTWG Charter 2018

     [25] https://www.w3.org/2018/05/timed-text-charter.html


   Nigel: Thanks everyone for contributing to that and working on
   it.

   Glenn: When does it go to?

   Nigel: 31 May 2020.
   ... One other thing for the notes only given the attendees
   today: there's no change in scope
   ... so any invited experts should _not_ be ejected and need to
   request re-invitation. If that
   ... does happen please let me know ASAP.

Clean up and refactor features (#688, #763, #789, #790, #791, #792,
#… ttml2#794

   github: [26]https://github.com/w3c/ttml2/pull/794


     [26] https://github.com/w3c/ttml2/pull/794


   Glenn: Summarising the changes, there were some comments on how
   to factor the condition
   ... features and I adopted as you suggested, pretty much
   exactly, and also for the rubyAlign-withBase
   ... I adopted your proposal. On the animate you had a question
   about if animate covers
   ... everything, and it was ambiguous to me as well. In a
   previous meeting we had discussed
   ... animate-related features and I said I would do some work to
   tie it to the calculation mode
   ... and that discrete and linear would be in the minimal
   features, and paced and spline would
   ... be separate features. I refactored animate to do that and
   to make sure that the animate
   ... feature did include those things. I took out the
   `#animate-calcMode`, `#animate-keySplines`
   ... and `#animate-calcMode` and added `#animate-minimal` which
   includes discrete
   ... and linear calc modes and by virtue of that implies support
   for keyTimes attribute.
   ... We don't need a separate feature for keyTimes since it is
   in the minimal set.
   ... The second thing I added was `#animate-paced` for paced
   mode.
   ... And I added `#animate-spline` which implies supporting the
   keySpline attribute.
   ... I redefined the `#animate` feature to include all those
   features plus `#animate-fill` and `#animate-repeat`.
   ... In my mind at this point animate is all wrapped up and
   doesn't make use of any negative
   ... definitions.
   ... And then the final comment is you had expected language
   about processor profiles and
   ... I commented that it doesn't work because there's no such
   thing as prohibiting a feature
   ... in a processor profile. If you don't require support then
   it is optional. If you require some
   ... superset of a set of features then it implies that all are
   present, and making them optional
   ... does not take them out so to speak. So there's no need to
   add something for processor
   ... profiles by my reading.
   ... I have a set of pulls stacked up pending this and Pierre
   suggested that we merge it ASAP.
   ... So I need it to go out quickly.

   Nigel: Thank you for that, good summary, it's substantive, and
   8 days old.
   ... [looks at the changes]
   ... Did you fix `#display-version-2` too?

   Glenn: Yes, and I spotted and fixed a typo in one of the links
   too.

   Nigel: Thank you!
   ... I have some concerns about merging early, because of the
   nature of the changes,
   ... but it's reasonable to ask in the circumstances.

   Cyril: I'm fine with it since it is early but not very early.
   It's been more than a week.

   Nigel: There's a lot to review here - I'm happy in principle
   with what you've described but
   ... need to look at the detail - if we can close the call early
   today then I will complete that
   ... review, but don't foresee any problems.

   SUMMARY: @nigelmegitt to complete review and add updated review
   status

Add features for standard and high dynamic range PNG images (#694,
#6… ttml2#770

   github: [27]https://github.com/w3c/ttml2/pull/770


     [27] https://github.com/w3c/ttml2/pull/770


   Glenn: The only outstanding piece on this is the reference. My
   opinion is we should make
   ... a normative ref to the WG Note. Given the loosening of
   policies from HTML5 I'm pretty
   ... sure that it is no longer a no-no. We can't define an HDR
   feature unless we can point
   ... to a normative reference to a format. There's no generic
   format. We either put it in with
   ... the WG Note as a normative ref or we don't include any HDR
   PNG feature.

   Nigel: Ok, @plhegar didn't get back to me.

   Glenn: It's been more than 14 days and we have @nigelmegitt's
   approval but nothing from
   ... Pierre or Mike. Since this is still hanging I didn't want
   to merge it without group input.

   Nigel: This is also related to a separate issue that I am not
   up to date on where I began
   ... working on a pull request and realised that we probably do
   not want luminanceGain
   ... to apply to PQ HDR image at all.

   Glenn: It sounds like we can't resolve this until that's worked
   through.

   Nigel: +1
   ... I've dismissed my review.

   Glenn: Does IMSC 1.1 use this?

   Nigel: IMSC 1.1 will need to be updated too.

   Glenn: Is it really orthogonal?

   Nigel: The impact comes from the comment you made Glenn about
   testing luminanceGain
   ... without supporting PQ PNG images.
   ... (also there's no way to make luminanceGain have no effect,
   i.e. be unity, where it is known
   ... that images generate PQ pixels already).

   Glenn: If we don't resolve this soon then there's a risk of
   needing a CR3 which I'm wary of
   ... because of the time implications.

   Nigel: Yes me too, I hope to be able to process this by the end
   of tomorrow so we can progress.
   ... Back to this particular topic, I think we may not need the
   png pq hdr feature at all,
   ... though we might need a processor feature that can support
   identification of pq pixels
   ... output from image processing, as defined by the ITU spec.
   That would get around the
   ... need to reference the WG Note.

   SUMMARY: Resolve #796 and then revisit this based on the
   conclusion to that issue.

Remove @style from animate and set (#703). ttml2#707

   github: [28]https://github.com/w3c/ttml2/pull/707


     [28] https://github.com/w3c/ttml2/pull/707


   Glenn: Nigel you asked for minimum two values in an
   animation-value-list and I did that.
   ... I changed the * to a + in the syntax.

   Nigel: Great, and I see that I made a later comment that if you
   do that then it would be
   ... consistent to complete the resolution of the issue by
   removing @style from the animate element.
   ... Did you do that as part of #707?

   Glenn: I did it in the schemas...
   ... Yes, it's been removed from both set and animate.

   Nigel: Looks good to me, I'll approve the pull request.

   SUMMARY: Discussed and agreed.

   github-bot, end topic

Describe generically compliant processors that support only external
… ttml2#755

   github: [29]https://github.com/w3c/ttml2/pull/755


     [29] https://github.com/w3c/ttml2/pull/755


   Glenn: It's tricky - in some places we have to use TTML without
   qualification and in others
   ... it is relevant to qualify as TTML2.

   Nigel: Yes!
   ... I need a bit of offline time to check through that but I
   think it's fine.

   SUMMARY: Review to continue offline

   github-bot, end topic

Exclude vertical length offset as 1st component in 2 component
positi… ttml2#769

   github: [30]https://github.com/w3c/ttml2/pull/769


     [30] https://github.com/w3c/ttml2/pull/769


   Glenn: I made a change in the syntax as Pierre suggested.
   ... Either we need to dismiss his review or wait on him for a
   few days. I'm willing to wait.

   Nigel: I assume he'll do that, and that seems like the right
   approach.

   Glenn: Basically the change was to match the CSS exclusions to
   syntactical combinations,
   ... by not allowing the excluded syntax at all.

   Nigel: Makes sense to me.

   SUMMARY: DIscussed in WG meeting, review to continue offline

   github-bot, end topic

Add explicit exceptions to ignoring element semantics with condition
… ttml2#772

   github: [31]https://github.com/w3c/ttml2/pull/772


     [31] https://github.com/w3c/ttml2/pull/772


   Glenn: I just did a commit last night to address comments.
   ... Nigel you pointed out that the use of content element
   wasn't sufficiently inclusive and
   ... suggested that we bring in all timed elements including
   region, so I introduced the
   ... term timed element. I had to review all the candidates for
   timed elements and decide
   ... what the distinguishing features were. I first thought
   timeContainer, but animate and set
   ... have begin and end but not timeContainer, since they don't
   have timed children.
   ... On the other hand everything had a begin, dur and end and I
   picked begin as a criterion.
   ... Then I changed content element ref to timed element so that
   should address your last
   ... comment and this should be ready to go.

   Nigel: Sounds good to me.

   Glenn: This just needs an approval - we've already passed 14
   days on this one.

   Nigel: OK, interesting we don't have a class that corresponds
   to these.

   Glenn: Not in the spec - in TTV we have an IsTimedElement that
   does that, so implementations
   ... have to do it. I'm loathe to add another class just for
   this purpose. A definition should
   ... suffice.

   Nigel: Okay, I'll review.
   ... There are 16 uses of "timed element" in the spec.

   Glenn: I just noticed that, I'll update to add links to it.

   Nigel: Since we refer to this before, was it deemed to be an
   obvious concept or did we
   ... inherit it from SMIL?

   Glenn: I don't recall inheriting it from SMIL, but our usage
   would be different anyway.

   Cyril: Timed Element is a concept in SMIL I think.

   Glenn: It could be but the glossary section is very weak. In
   any case now that we have
   ... introduced timed element we should link those 16 places
   back to the definition now that
   ... we've added a term.

   Nigel: +1
   ... Notices we should take care with 12.4

   Glenn: Yes

   Nigel: Aside from that, I think this looks good.

   SUMMARY: @skynavga to update to include references to the timed
   element term, then review to continue.

   github-bot, end topic

Clarify distinction between validation processing, validation
process… ttml2#777

   github: [32]https://github.com/w3c/ttml2/pull/777


     [32] https://github.com/w3c/ttml2/pull/777


   Glenn: I did a commit last night in which I think I addressed
   Nigel's comments.

   <glenn>
   [33]https://github.com/w3c/ttml2/pull/777/commits/4aaf65d902fc7

   0f374e31751074a18d26389f6f2

     [33] https://github.com/w3c/ttml2/pull/777/commits/4aaf65d902fc70f374e31751074a18d26389f6f2

   Nigel: [reviews in real time] Looks good to me.
   ... I've approved.

   SUMMARY: Pull request satisfies merge requirements.

Collapse language for style application to paragraph text nodes; add
… ttml2#803

   github: [34]https://github.com/w3c/ttml2/pull/803


     [34] https://github.com/w3c/ttml2/pull/803


   Glenn: I added a comment to this.

   Cyril: Can we add a link from the sentence in 8.1.5 to the
   process for creating anonymous spans?

   Glenn: Yes, and come to think of it we should add the same text
   to the span element to
   ... make it complete. Right now it is incomplete.

   Cyril: I don't want it to look like there's a separate
   procedure.

   Glenn: That gives me a tbd on this before you sign off on it
   Nigel

   Nigel: OK
   ... Should we add a note pointing the reader to anonymous spans
   beneath the new text?

   Glenn: I don't want another place where we paraphrase what the
   construct anonymous span
   ... procedure does.

   Nigel: I was thinking of a note with a reference, but I take
   your point.

   Glenn: The terms anonymous span and span already take you to
   the right definitions.

   Nigel: Yes, if you add that anonymous span text from p to span
   then yes, I'm okay with that.

   SUMMARY: Duplicate anonymous span text from p element into span
   element (for @skynavga) and reference the [create anonymous
   span] procedure from both.

Add xml:base to core vocabulary (#804). ttml2#808

   github: [35]https://github.com/w3c/ttml2/pull/808


     [35] https://github.com/w3c/ttml2/pull/808


   Glenn: This adds `xml:base`. Previously in TTML1 the `features`
   and `extensions` elements
   ... admitted `xml:base` and those were unusual in that we
   defined a default value in the
   ... element information item that specifies using the TTML
   feature namespace and the extensions
   ... namespace respectively. Those were kind of special uses
   that had a default.
   ... This PR and issue is for, now that we have URLs in a
   variety of other places such as
   ... xlink:href and the source element and audio, data and
   image, we potentially have some
   ... uses that are related to the media query support in the
   condition function for media functions,
   ... my conclusion was we need to add `xml:base` to the core
   attributes list so it is everywhere.
   ... Now `xml:base` is hierarchical so you can have multiple
   relative levels. It can build up
   ... hierarchically from the most nested reference to the root
   level element. You need to
   ... populate it everywhere (ability to populate).
   ... Especially if you're embedding content that has some URLs
   in it you might nest that in
   ... another document and put a relative base on it at the
   highest level node. It turns out to
   ... be quite useful and is supported in SVG and SMIL as well.

   Nigel: Did you fix Cyril's issue about isd:css and isd:region
   too?

   Glenn: Yes. I know Cyril had suggested just supporting on the
   root level but as you see that
   ... won't quite work.

   Cyril: I understand the feature, I don't think it's a priority.
   You could default it to the base
   ... of the document itself.

   Glenn: That is the default default if there are relative URLs
   in the document with no xml:base specified.
   ... We don't have to say anything to support that.

   Cyril: I don't have a strong preference. It's mainly useful for
   images and audio content right?

   Glenn: Exactly.

   Nigel: I don't have strong view either, but don't have a
   particular use case. I don't think it
   ... is especially harmful. Is there a profile feature for it?

   Cyril: There is #base and #base-version-2

   Nigel: Ok

   <cyril>
   [36]https://rawgit.com/w3c/ttml2/0c93c4dfa88e85a61d1c2cf1bae9a5

   30c1e7e25c/index.html

     [36] https://rawgit.com/w3c/ttml2/0c93c4dfa88e85a61d1c2cf1bae9a530c1e7e25c/index.html


   Glenn: I defined it that way because we already had base in
   TTML1 but with no feature so
   ... I defined in TTML2 a feature that mapped to the original
   TTML1 support for base and then
   ... extended it with the version-2.

   Nigel: Makes sense.

   Cyril: I think we should move on from this - it was opened
   yesterday.
   ... Seems consistent, not harmful, we should approve if there's
   no objection. I would like
   ... some input from the SMPTE image users to see if they have
   any views on this.

   Glenn: Yes, I'm not asking for early merger on this.

   SUMMARY: Offline review to continue.

   github-bot, end topic

Add #unicodeBidi-version-2 feature designator (#679). ttml2#759

   github: [37]https://github.com/w3c/ttml2/pull/759


     [37] https://github.com/w3c/ttml2/pull/759


   Glenn: Nigel you made a statement about this but did not
   approve.

   Nigel: Yes, that was 2 weeks ago, pending a discussion of the
   approach to defining features
   ... by reference to their TTML1 definition. We had that
   discussion and agreed to proceed
   ... on that basis so I can now complete the review of this pull
   request.
   ... [does a rescan] Looks good to me.
   ... I've approved it.

   SUMMARY: Pull request meets criteria for merging

Add and update element derivations (#380). ttml2#805

   github: [38]https://github.com/w3c/ttml2/pull/805


     [38] https://github.com/w3c/ttml2/pull/805


   Glenn: I don't have any reviews on this yet.

   Cyril: The reason I didn't review it is I don't really consider
   it necessary. There's no impact
   ... if there's a bug in this one.

   Glenn: Exactly, this is a non-normative appendix.

   Cyril: I can approve it if you want but I thought Nigel was
   best placed to do it.

   Nigel: I need more time to review this.

   Glenn: That's fine with me - I just need a review. It's an
   editorial pull request that's only 2
   ... days old, so there's a day to go minimally before merge
   anyway.

   Nigel: OK I'll take a look.

   SUMMARY: Offline review to continue

   <glenn>
   [39]https://github.com/w3c/ttml2/issues?utf8=%E2%9C%93&q=is%3Ai

   ssue+is%3Aopen+milestone%3ACR2+-label%3A%22pr+open%22

     [39] https://github.com/w3c/ttml2/issues?utf8=✓&q=is:issue+is:open+milestone:CR2+-label:"pr+open"

   github-bot, end topic

CR2 issues with no pr open label on them

   [40]https://github.com/w3c/ttml2/issues?utf8=%E2%9C%93&q=is%3Ai

   ssue+is%3Aopen+milestone%3ACR2+-label%3A%22pr+open%22

     [40] https://github.com/w3c/ttml2/issues?utf8=✓&q=is:issue+is:open+milestone:CR2+-label:"pr+open"

   Glenn: I've marked a couple of them for agenda

Time containment semantics for smpte time base. ttml2#377

   github: [41]https://github.com/w3c/ttml2/issues/377


     [41] https://github.com/w3c/ttml2/issues/377


   Glenn: Nigel, you're original complaint was that we prematurely
   deprecated the use of
   ... the sequential time containment in smpte discontinuous mode
   and you have argued that
   ... there is a potential interpretation of that. I argue that
   even if that is the case then it
   ... doesn't make any sense to use it and it shouldn't be used
   anyway.
   ... In my mind smpte discontinuous indicates that there is no
   time container at all.

   Nigel: I don't think there's no time containment.

   Glenn: For example if you have a span in a p and the span says
   begin=0s and the p says begin=10s
   ... for me the 0s on the begin relates to the document timeline
   not to the p.
   ... Any time you find a time in a smpte discontinuous document
   then it relates to the
   ... document context. This is from markerMode. The problem with
   what you're suggesting
   ... Nigel is that it backs out that. Under markerMode it says
   that time expressions must not
   ... be calculated etc. in discontinuous mode. All time
   expressions are interpreted as time
   ... events which cause a temporal interval to begin or end
   accordingly.

   Nigel: I don't disagree with that but my point is that time
   expression calculation is orthogonal
   ... to time containment, and that there is a logical processing
   model for sequential time
   ... containment with smpte discontinuous, treating the time
   expressions as events.
   ... I don't believe that there is any data presented to
   deprecate this potential usage.

   Glenn: If we take out the deprecation, I don't really want to
   tweak this language or add
   ... more language?

   Nigel: I don't think we need to do anything particular to the
   spec and I wouldn't prioritise
   ... this niche use case, just back out the deprecation.

   Glenn: Is this editorial?

   Nigel: Although we apparently did not have consensus for this
   when #647 was merged
   ... in February, this is a substantive change relative to CR1
   unfortunately.

   Glenn: Okay I can accept backing out the deprecation, I may ask
   for early merge next week.

   SUMMARY: Back out the deprecation of seq time containment in
   smpte discontinuous

Negative feature designators aren't future proof. ttml2#697

   github: [42]https://github.com/w3c/ttml2/issues/697


     [42] https://github.com/w3c/ttml2/issues/697


   Nigel: I still have the action on this.

   Glenn: To some extent #794 overtakes this because we are
   already backing out some
   ... negative feature designations. I'm not sure if there are
   potential action items.

   Nigel: Let me keep it and think further on this please.
   ... The action on me is to demonstrate that there is a specific
   problem.

   Glenn: The only remark I have is that one of the reasons we use
   the phrase "all defined values"
   ... is that not all values are enumerable, e.g. floating point
   values, and the primary condition
   ... expressions are infinite in their number of possibilities,
   so we can't enumerate every
   ... value set.

   Nigel: There are ways to group value sets finitely.

   Glenn: In the condition refactoring, where you suggested using
   "non-function" expressions,
   ... there probably isn't any other way to do it.

   Nigel: Ok the action is still with me.

   Glenn: My point is even if you think we'd like to do this I
   don't think we can completely
   ... do what you're suggesting, in the case of some infinite
   value sets.

tts:rubyReserve length component semantics ttml2#779

   github: [43]https://github.com/w3c/ttml2/issues/779


     [43] https://github.com/w3c/ttml2/issues/779


   Cyril: Glenn can you clarify that we harmonised rubyReserve
   with rubyPosition using
   ... `<annotation-position>`? Looking at the CR spec I couldn't
   find it.

   Glenn: There's an optional length component in rubyReserve.
   ... The set of keywords that are defined there are equal to or
   a subset of `<annotation-position>`.
   ... We took out around and between.

   Cyril: Did we change the examples?

   Nigel: [checks spec] There's no mismatch between the examples
   in rubyReserve and the syntax.

   Cyril: OK, sorry, I was looking at the wrong version.

   Glenn: The example does need to be updated - around and between
   have gone.

   Nigel: Sorry, I also looked at the wrong version.

   Glenn: It looks like I just need to remove the around and
   between examples.

   Cyril: OK, now about the behaviour or ruby, line area and
   lineHeight.
   ... You clarified that the rubyReserve area is parented to the
   line area.

   Glenn: Correct.

   Cyril: But I remember that the CSS WG said that you also had to
   set the line-height and that
   ... ruby-reserve did not affect the line height. Is that the
   case in TTML2 as well?

   Glenn: I avoided going into the details of this in the spec.

   Cyril: so it's implementation specific?

   Glenn: Yes.

   Cyril: Why don't we do the same with rubyReserve?

   Glenn: TTP for example increases the line height based on the
   concept that the definition
   ... of normal under line height maps to the per inline height
   rectangle in XSL-FO and that
   ... is defined in such a way as to increase the line height on
   the per line area basis based on
   ... the glyph areas contained in that so that the ascender,
   descender and half leadings on
   ... both sides of every glyph area are included in the line
   height for that particular line.
   ... The height of individual areas in "normal" varies based on
   what is inside them. The model
   ... there is to extend the line height to enclose the
   descendants. I use the same model, if
   ... lineHeight="normal" (including default) it will increase
   the line height of a box that has
   ... ruby to include the ruby annotation inline areas. I avoided
   writing this into the spec at
   ... this point. One thing you are suggesting is that we add a
   note maybe that it is implementation
   ... dependent what effect rubyReserve has on lineHeight?

   Cyril: I'm not sure if that is what I am suggesting. I am
   trying to understand how it works.
   ... If I cannot understand it probably other readers cannot
   understand how it works.

   Glenn: Interestingly Pierre is just mapping to CSS and letting
   CSS do it. What I implemented
   ... is basically compatible with that. CSS doesn't define those
   details. It's basically what is
   ... implemented in the wild is the de facto standard.
   ... It would take a lot of work to define those requirements.

   Cyril: I'm fine with not specifying it and maybe in a future
   version doing that when we have
   ... converged on a processing model.
   ... Pierre is saying that the length field is over-specified?

   Nigel: I think we need Pierre here for that.

   Glenn: My interpretation is that he has some issue with how we
   define the default value
   ... for length.
   ... We have the problem of length with lineHeight too, which is
   not dependent on font size either.

   Nigel: OK so now we have the problem in two places!
   ... Given the time and that this issue was raised by Pierre who
   is absent, we should not
   ... continue with this issue.

   github-bot, end topic

Use of maximum descendant font size in normal line height
computation. ttml2#806

   github: [44]https://github.com/w3c/ttml2/issues/806


     [44] https://github.com/w3c/ttml2/issues/806


   Glenn: I would like to spend 5 minutes on this for the record
   ... The issue is lineHeight - what does "normal" mean?
   ... We had some language in TTML1 that said the computed value
   is no less than the font
   ... size that applies to the element and its descendant
   elements. When we recast that in TTML2
   ... we inadvertently omitted mention of the descendant
   elements.

   Nigel: No, we discussed it and decided that we didn't need it.

   Glenn: Thanks for reminding me, I need to go back to the notes
   on that.
   ... I decided to re-review the way that XSL-FO defines this,
   and the CSS semantics, and I
   ... concluded that TTML1 semantics do not match CSS 2 or XSL-FO
   and TTML2 semantics
   ... match none of them as defined. I marked this as a bug and
   something we need to deal with.
   ... I was going to maybe today or tomorrow post a pull request
   to deal with this. The main
   ... problem is that the current algorithm leads you to the
   conclusion that you can set a
   ... uniform line height that is resolved from normal and that
   it applies to every line
   ... irrespective of the inline areas on each line. In the
   XSL-FO language it says it should be
   ... the minimum required to enclose the paragraph's requested
   line height and the line height
   ... for each of the inline areas within the line area. In other
   words different line areas may
   ... have different heights based on lineHeight="normal". The
   current text does not do what
   ... CSS2 does or what XSL-FO says.
   ... We're inconsistent.

   Nigel: I recall Andreas making a presentation to us in a face
   to face meeting about this,
   ... and pointing out that the line stacking strategy we use in
   TTML means that lines can
   ... never overlap each other.

   Glenn: I dispute that, and will have to go back and check.
   ... "normal" is the most used value, and I'm pretty sure that
   the expectation would be the
   ... same as in CSS, but that is not how it is specified now.
   ... I don't know if say imsc.js would be able to do what the
   new language says.

   Nigel: I would advocate looking for line stacking strategy and
   go back to where we discussed this before.

   Glenn: In the case of "normal" you don't get bleed over between
   lines, but you might with a number.

   Nigel: I thought the same line stacking strategy applies even
   with a number.

   Glenn: If that's the case then XSL-FO would be inconsistent
   with CSS2. I would need to look at that.

   Nigel: The line-stacking-strategy is line-height, regardless of
   the value of tts:lineHeight.

   SUMMARY: @skynavga to continue investigating

   github-bot, end topic

Meeting close

   Glenn: We covered a lot today so thank you for that. I look
   forward to the pull request reviews.
   ... #794 is my highest priority if you can take that into
   account.

   Nigel: OK, thanks both, next meeting same time next week.
   [adjourns meeting]

Summary of Action Items

Summary of Resolutions

   [End of minutes]
     __________________________________________________________


    Minutes formatted by David Booth's [45]scribe.perl version
    1.152 ([46]CVS log)
    $Date: 2018/05/31 16:46:33 $

     [45] http://dev.w3.org/cvsweb/~checkout~/2002/scribe/scribedoc.htm

     [46] http://dev.w3.org/cvsweb/2002/scribe/







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Received on Thursday, 31 May 2018 16:48:01 UTC