Meeting minutes
This meeting
Nigel: Today we have some IMSC topics: PR transition, vNext requirements window,
… and ARIB issues. We also have a placeholder for TTML2 IR but I don't think there's
… much to discuss there.
… AOB or points to remind the Chair to make sure get covered?
Pierre: Admin: can we talk about the pull requests that are updating links on the published Rec.?
… They say the PR is not for release. Can we take 5 minutes on this.
Nigel: Right, on IMSC?
Pierre: Yes, old IMSC, 1.0.1, 1.1
IMSC 1.2 CfC to request transition to PR
Nigel: Reminder that the CfC is open until 5th June.
CfC to request transition of IMSC 1.2 to PR
Nigel: Anything to raise on this topic?
IMSC vNext requirements window
Nigel: 2 current drivers for this (so far):
… 1. Netflix requirements provided by Cyril a few weeks back
… 2. ARIB liaison
… Of course there may be other requirements.
… Historically we have opened a window for people to register new requirements,
… and I propose doing the same thing again. The question is the time window for
… doing this.
… Any proposals?
Pierre: It would help if we as a community try to guess what the scope would be.
… It's hard before calling for requirements, but it would help on the timing.
… We have contributions from Disney and Netflix that are very specific.
… We have ARIB which are very specific too and potentially the changes will be more significant.
… Do we foresee anything else?
Nigel: I don't think I'm aware of any right now.
… Something else that's relevant is that CSS is working on Ruby stuff at the moment
… so we potentially have a sync point with their work.
<atsushi> (sorry for delay of my email on these, Nigel)
Nigel: It feels that there may be a need to get agreement with multiple parties who might
… take a while to respond.
Pierre: That's my feeling too.
… We could adopt a new more flexible process where we could issue regular snapshots
… and address issues as they come up, and decide to go to Rec or not Rec based on
… how much we have.
… If we do the traditional process for Rec like we did with IMSC 1.2 then it will be many months.
… Question for Netflix is how urgent the fontShear work is for Rec publication.
Cyril: Good question, I would say the sooner the better because I want to avoid divergence
… between actual implementation and content deployed.
… But alignment with CSS is important, at the same time.
Pierre: Thinking out loud, a more iterative process is not incompatible with the idea of
… a requirements window for establishing the scope of what we are doing.
… We could freeze them now!
Nigel: Not sure that's wise!
Pierre: I'm saying a short period, give people 2 months rather than 6.
Atsushi: Comment on font shear. In i18n JLREQ task force we discussed font shear in
… Japanese. But our knowledge was that font shear is not used in Japanese typography
… so the TF decided not to state any requirement for font shear in JLREQ.
… There is a common way to share font in Japanese typography used for publishing,
… but we haven't had mutual agreement to state something to CSS WG yet. Just for information.
Cyril: That's interesting because it is exactly the opposite of the conversation I had with
… the CSS WG member from Google who is from Japan. Koji Ishi maybe. The way we want
… to do shearing in general is exactly the way it is done in Japanese typography so we
… probably need to resolve that.
Atsushi: I think he mentioned the common way that font shear is done in recent Japanese
… books. For input to CSS WG we may need to state something from some sort of
… Japanese group. We failed to get to agreement in the JLREQ TF. To have some statement
… we have to get input from a digital publishing group in Japan. I think I need to go back
… to W3C Keio with this to complete the coordination.
Nigel: Another question about a requirements gathering phase is how we make it known
… to the world. For example liaisons, as we have done previously, or a W3 blog post etc
… It seems that some folk have come to us without any need for this.
… Can we say now that the requirements window is open, and think about the closing date
… and comms for it in the next few days?
PROPOSAL: The window for new requirements for future versions of IMSC after 1.2 is now open.
Nigel: Any objections?
<atsushi> +1
Cyril: no
Pierre: Sounds good to me
Resolution: The window for new requirements for future versions of IMSC after 1.2 is now open.
<atsushi> (+1 means go ahead w/ no objection)
Nigel: Thank you.
[WR/ARIB] Mixture of text and image w3c/imsc#543
github: https://github.com/w3c/imsc/issues/543
Vladimir: Just for clarification, can we clarify exactly what they mean by inline graphics?
… I'm not sure what they really mean.
Nigel: I understand it to be the kind of requirement where a company logo is inserted as
… a graphic inline with text.
Vladimir: If someone wants to use a PUA code point in a user defined font for this, then
… there is nothing we can do to stop them. I would say that would be a pretty unobjectionable
… use of PUA codes because that's exactly what they're for. It's not going to hinder text
<cyril> this IMSC requirement has an example https://github.com/w3c/tt-reqs/issues/15
Vladimir: processing or editing or search. I think that is not really a concern.
… My concern was about GSUB substitution when you need to select the right form.
… Anything that would be used to avoid doing standard processing for truly text content.
… If they want to simplify things by missing some functionality I would say that's a bad idea.
… They say that if GSUB is used before IVS is used then, it sounds like they want to simplify
… by avoiding the need to do it. I think they just want to use PUA to see something they
… want to be displayed. I would say that is a bad idea. It might work in a closed system
… where the Timed Text is authored in the same environment but as soon as you attempt
… to make it something more interoperable then you can't expect everyone to do it the same way.
Nigel: I wanted to note that PUA use can impact text processing, for example if a company
… name is being substituted for its logo, then you might reasonably want to do things like
… Text to Speech of the text,
… Searching by text name,
… all before any substitution. If PUA is used that really will break those use cases.
… I think that is why we got to the point of using GSUB as a good idea before.
Vladimir: I absolutely agree with this. I don't think that PUA should be used in place of
… a company name, because the implementation will break.
Cyril: I agree with what Vlad said. I talked to my Netflix experts and they are of the same
… opinion that we should avoid PUA as much as possible for all the reasons that were
… explained. I am wondering how ARIB got the notion that we require GSUB, because I
… don't think it is mentioned in the spec. Secondly maybe we should add something
… to limit the complexity of the implementation. I don't know if we can, for example limit
… the font functionality required for IMSC. Are there profiles for this? I don't know.
Vladimir: Any attempt to do something to simplify implementation to let them off the hook
… of a specific standardised feature, I think is not a good idea, because that feature may
… manifest itself elsewhere that we cannot predict.
… If normal text comes in and implementations drop a standardised case then
… preprocessing would be needed. The short answer: I don't think it's a good idea to
… simplify implementations if it goes against the standardised feature set.
Pierre: I think what we should do is get actual samples. It just occurred to me that there
… are no examples of what they are trying to do. We should try to see how this works
… in practice. We had a long thread on what we wanted to do with GSUB and we should
… try it and assess how well supported and how easy it is.
… We're at the point where we need to try it before we come up with a solution.
… I would actually go back to ARIB and request a sample.
Nigel: That's a really good idea
Cyril: Are there tools that allow us to easily create fonts with a GSUB substitution?
Vladimir: Any font tool - most of them allow substitutions. You write your own rules as
… a code entry, to substitute a sequence of glyphs. You don't know what those glyphs
… represent. You just set a rule. Any sequence of input can be substituted. For example
… a company name substituted by a logo is perfectly possible.
… For example the Zapfino font, on most Macs I think, has a substitution entry that
… substitutes the name of the font for the ligature. They do it just to showcase it.
… You can substitute a ligature or anything else.
Nigel: That's an input sequence of code points?
Vladimir: The input is a sequence of unicode text points.
… Then map those to glyph ids.
… Then most of the time the substitution rules apply to those glyph ids
… Then you have character codes, and depending on location and many other rules, the
… base glyph can be substituted by something else.
… For example in Arabic, a positional variant; for Japanese, a variation sequence definition.
… If you have a ligature for example for a sequence of glyphs, that is applied to the glyph
… id sequence mapped from the character codes.
… You end up as part of this process as one code point entry mapped to a glyph that is
… one of a number of possibilities.
Andreas: A question re GSUB and PUA. Regarding the concerns that Nigel mentioned
… for example using text for a screen reader, where is the difference between GSUB and
… the use of PUAs? Both are not very accessible.
Vladimir: It's exactly opposite. Your accessibility is defined by the code point sequence.
… Then your Unicode sequence does not change and is used by the screen reader.
… The font level modifications will only affect visible display, not the content itself.
… That is why this is probably the only accessible way of doing things.
… If you move visualisation decisions upstream and simply use a PUA code point to map
… to a particular glyph, then you break accessibility, because now your screen reader has
… no idea what that is.
Andreas: And there is no requirement that the mapping of the glyphs that people will read
… will go with what is specified by the code points.
Vladimir: Exactly, which is why PUA should be avoided unless there is something that has
… no meaning for somebody who cannot see the text.
<cyril> Zapfino example: data:text/html,<div%20style="font:%2048px%20Zapfino">Zapfino<br>Zapfin%20o
Vladimir: If you have "company name, logo" where logo is a PUA then that's fine if the screen reader
… ignores the PUA but if the company name is omitted then it will not be accessible.
Nigel: This reminds me of presentation-scheme based fallback options, and I think we
… should avoid those if we possibly can.
Vladimir: Yes exactly, and that is the basis of the Unicode choice to let font engines
… do substitutions where needed so that they only affect visual presentation.
Cyril: I asked my font expert if there is a limit to the length of the substitution, and he
… told me it can be very long, like 30 glyphs. Is there a limit?
Vladimir: I don't think so, only practical limitations.
… Substitution tables can define a chain of substitutions and it is only limited by
… complexity and how far a font designer wants to go.
Cyril: Vladimir you were asking for an example. Earlier on IRC I posted a link to one of the
… requirements that we have. Nigel showed an example of the Twitter logo inline with the
… text.
Nigel: Thanks for digging that out!
Cyril: It's w3c/tt-reqs#15
Pierre: That's the issue that led to the current situation in IMSC and TTML.
… It would be good to get input from ARIB with sample text and corresponding render.
Vladimir: Yes, for example if someone wants to define the logo as a PUA code in addition
… to the name Twitter, then that would be fine.
… But if you drop the name and only use the PUA for the logo, it breaks accessibility.
… Better to do it as a font substitution, for visual presentation.
… As far as content sequences are concerned the name Twitter is still there.
Cyril: Also graceful degradation, in case the font engine doesn't support substitution.
Vladimir: I agree. Any time substitution fails you see the original unsubstituted text.
… For company names that's fine. For Devanagari almost everything is a substitution, so
… the presentation would fail.
Cyril: I'm trying to get back to the ARIB issue and understand what exactly they wanted.
… They end by saying to consider that PUA is a simple implementation and a clear indication
… on the use of GSUB would be helpful.
… On the first point I think we disagree with them. We don't want to recommend it.
Pierre: I can't even conclude that without seeing what they want to do and making sure
… that we can do it.
Cyril: I agree that would be useful. I wonder if we should say that PUA is not recommended.
Pierre: Imagine they come back with a PUA example where we can't give a better alternative.
Cyril: You would want to say at this stage we cannot ...
Pierre: I would like to get a solid example.
Cyril: Yes, okay that's good.
Pierre: If they cannot produce an example that also informs us a lot.
Vladimir: 2 final comments. One on what was just discussed. I don't think we can do anything
… to stop them using PUA codes. If someone decides to use it we cannot prevent it.
… On the substitution side, trying to define something in the TTML spec, all we can say
… is we expect font engines to be conformant with the OFF standard.
… If they support the standard then that's not a concern.
Cyril: I don't think we want to explain how substitution works in general, but maybe
… an example of how to use substitution to explain how it can be used to produce
… inline graphics could be useful in TTML.
Vladimir: That would be fine [assuming that the spec is stuck to]
Cyril: I agree.
SUMMARY: TTWG to request ARIB for examples, and consider adding a substitution example to IMSC or TTML.
Nigel: I think I heard no proposals for substantive language about support for particular
… features.
Cyril: I think Pierre [who left a moment ago] was saying we should wait for examples first.
<Vladimir> just an illustration to my previously used example: https://www.myfonts.com/fonts/linotype/zapfino-extra/
Cyril: The action is to request this from ARIB as part of a general response?
<Vladimir> the whole name is substituted with the glyph that represents the font name
Nigel: I would prefer to wait until we have covered the other ARIB issues but if it is going to
… be many weeks then I would prefer to do it sooner.
Cyril: Yes that makes sense.
<cyril> data:text/html,<div%20style="font:%2048px%20Zapfino">Zapfino<br>Zapfin%20o
Meeting close
Nigel: Thanks everyone. We're out of time so I'll adjourn now.
… We didn't manage to get to Pierre's AOB point, so hopefully we can cover that off-line.
… [adjourns meeting]