Usage pattern for specifying an image's alternate text.

[skynavga]

IMSC1.1 [1] states that

A div element that contains a child image element SHOULD contain a metadata element containing an altText named metadata item that is a Text Alternative of the image resource referenced by the image element.

This is inconsistent with the intended usage shown in TTML2 [2], which would have

<div>
  <image ...>
    <ttm:item name="altText">Alternate Text</ttm:item>
  </image>
</div>

instead of the current recommendation which would have

<div>
  <metadata>
    <ttm:item name="altText">Alternate Text</ttm:item>
  </metadata>
  <image .../>
</div>

The problem with this latter usage is that the alternate text is not semantically associated (by document structure) with the image, but instead, with the div.

Apparently I did not catch this earlier when IMSC1.1 was being published. I would suggest this be addressed in IMSC1.2 by deprecating the current recommendation in favor of a new recommendation based on the first usage example shown above.

[1] https://www.w3.org/TR/ttml-imsc1.1/#image-ttml-image
[2] https://www.w3.org/TR/2018/REC-ttml2-20181108/#xml-lang-example-1

[palemieux]

The problem with this latter usage is that the alternate text is not semantically associated (by document structure) with the image, but instead, with the div.

I am not convinced it is a fatal issue since, in Image Profile, each div contains zero or one image element. This also parallels the use of ittm:altText in conjunction with smpte:backgroundImage.

If we decide the current approach was an error, then IMHO it should be changed in IMSC 1.1.

[skynavga]

I didn't say it was a fatal issue, but I do believe it was an error, and not consistent with the semantics of metadata association as described shown in examples in TTML. I don't have a strong opinion as to where it gets addressed, but it should be addressed somewhere.

[skynavga]

As for paralleling the use of smpte:backgroundImage, that was an attribute on div, so it made sense there, but image is a child of div, so it is not quite the same.

[nigelmegitt]

Sorry for the not very helpful comment, but I have a half-recollection that we discussed this point before arriving at the current solution. I don't have time to do the archaeological dig to find that right now though.

[nigelmegitt]

@skynavga we'd like to be able to resolve this before or during Thursday's call if possible.

[skynavga]

@nigelmegitt I don't see a proposed resolution.

[palemieux]

@skynavga The proposal is to do nothing.

[css-meeting-bot]

The Timed Text Working Group just discussed Usage pattern for specifying an image's alternate text. imsc#490, and agreed to the following:

• RESOLUTION: We will not address this in IMSC 1.2 but leave on the backlog for potentially fixing in some future version.

The full IRC log of that discussion

<nigel> Topic: Usage pattern for specifying an image's alternate text. imsc#490
<nigel> github: https://github.com//issues/490
<nigel> Nigel: This has been in IMSC since 1.1 hasn't it?
<nigel> Pierre: Correct, and it follows the pattern for when smpte:backgroundImage is used, which is why we ended up here.
<nigel> .. Another data point is we should really refrain from making changes to image profile unless absolutely necessary.
<nigel> .. Maybe in the future there will be some new requirement for the image profile that will give us an opportunity to
<nigel> .. correct these things. At this point I don't think it would be worth the trouble and it would be particularly disruptive.
<nigel> .. I'm happy to close it or deschedule it and defer it to a backlog so we don't forget about it.
<nigel> Nigel: That was going to be my suggestion.
<nigel> Pierre: I propose moving to the backlog.
<nigel> Nigel: Any other views on this? Any problems saying we may deal with it one day but not right now?
<nigel> Pierre: An advantage of doing this is that if someone runs into this and starts raising an issue they should be able to
<nigel> .. find it in the open issues list fairly quickly, and comment on it.
<nigel> Nigel: I'm hearing no objections - obviously Glenn is absent but he has the opportunity to comment during the review
<nigel> .. period as per our Decision Policy.
<nigel> RESOLUTION: We will not address this in IMSC 1.2 but leave on the backlog for potentially fixing in some future version.