Generic processor conformance too strict.

[nigelmegitt]

See #594 (comment)

[skynavga]

@nigelmegitt this is not a problem; see #594 (comment)

[nigelmegitt]

@skynavga I can see why you thought that, please see additional explanatory #594 (comment)

[css-meeting-bot]

The Working Group just discussed Generic processor conformance too strict. ttml2#673, and agreed to the following:

• SUMMARY: Issue discussed and mutual understanding improved, more thought needed.

The full IRC log of that discussion

<nigel> Topic: Generic processor conformance too strict. ttml2#673
<nigel> github: https://github.com//issues/673
<nigel> Nigel: The summary of this is that it is reasonable to have a content profile prohibit use
<nigel> .. of features that are mandatory for generic processor conformance.
<nigel> Glenn: I don't think we can make them optional because they're mandatory in TTML1.
<nigel> .. We have another issue that's related, about making profile-version-2 optional: #683
<nigel> .. In pull #755 I proposed some language in the claims section that allows for conformance
<nigel> .. without supporting the mandated features. I think that applies in this context too.
<nigel> Nigel: Yes, I see that.
<nigel> Glenn: You're saying you might have a profile that doesn't support things that seem to be
<nigel> .. mandated by the official minimum profiles, which is not unreasonable and has been done,
<nigel> .. for example EBU in excluding the profile features. So your additional comment will be
<nigel> .. dealt with by pull #755.
<nigel> .. Basically a processor can be a ttml processor but cannot claim conformance as defined
<nigel> .. by the conformance clauses.
<nigel> .. It can claim generic conformance but not one of the two special ones.
<nigel> Nigel: But §3.2.1 bullet 4 requires support for everything listed as M in §E.2.
<nigel> Glenn: That doesn't mandate support for e.g. #profile.
<nigel> Nigel: The way I read it is does, because step 4 must be satisfied, and doesn't refer to
<nigel> .. any profiles, just the specification, and it clearly relates to things listed as M in §E.2, which
<nigel> .. includes `#profile`.
<nigel> Glenn: I see what you mean. It's possible that the note is wrong in the context of such a
<nigel> .. content profile not requiring support for everything listed as mandatory.
<nigel> Nigel: Good, we're on the same page in terms of the issue at this point.
<nigel> Glenn: Either you have to implement everything even if use is prohibited by a profile, or
<nigel> .. we somehow relax that language to permit the creation of an implementation that doesn't
<nigel> .. require support for all those mandatory features.
<nigel> Nigel: Yes
<nigel> Glenn: An option is to have a lower case ttml processor conformance state that does not
<nigel> .. include Generic Processor Conformance.
<nigel> .. Back in TTML1 days we had a huge discussion about minimally required features. The
<nigel> .. first chink in that was when EBU-TT was created. Just a historical fact.
<nigel> .. Now with IMSC we seem to be following the same path.
<nigel> .. It looks like we'll need some more thinking on this.
<nigel> SUMMARY: Issue discussed and mutual understanding improved, more thought needed.