The source of alt text in embedded image media is not clear

brain dump slack conversation from today. Use this to update the issue summary.

andrewmacpherson 4:11 PM
Related issue, not so major though. Let's say an author embeds an image, and accepts the default alt text from the media entity, because it's appropriate in the context.But later, another editor updates the default text on the media entity.

phenaproxima (he/him) 4:12 PM
I believe it would inherit it, in that case.

andrewmacpherson 4:12 PM
When you accept the default alt text, the <drupal-media> tag doesn't have an alt attribute. So the fact that they have accepted the default isn't really explicit.
Now when the default alt on the media entity is updated, it propagates to all instances which have not explicitly overridden it?
That could be risky. When the author originally accepted the default alt text, it was appropriate to the context. If the default alt stored with the media entity changes, it may no longer be appropriate for the context.
That's kind-of almost in the territory of accidental data loss.

phenaproxima (he/him) 4:16 PM
@wimleers (he/him) Any opinion on this? ^^

andrewmacpherson 4:16 PM
I have a feeling ATAG has something to say about this, will check later.

phenaproxima (he/him) 4:17 PM

@andrewmacpherson That feels like a documentation issue to me, almost. Media is built on entity references; entity references are centralized by their nature.

andrewmacpherson 4:17 PM
A different approach would be to explicitly store the <drupal-media alt>` in all cases, so there text the author accepted survives.

phenaproxima (he/him) 4:17 PM
We are introducing this new pattern here, of a centralized thing that can be decentralized on request.

andrewmacpherson 4:18 PM
but that's at the cost of making it more difficult to propagate changes in the default alt text.

phenaproxima (he/him) 4:18 PM
Exactly.
So basically…which is a better default behavior? (edited) 
It’s not clear.

andrewmacpherson 4:19 PM
Swings and roundabouts, but I think the safer option is to preserve the alt text that the author approved for the embed instance. Less risk of nasty surprises or unintended content changes.

phenaproxima (he/him) 4:20 PM
@andrewmacpherson I think, on a technical level, this would be a very trivial change for us to make. However, we’d need to validate this with UX and the PMs.
Another option would be to make it configurable.
Which would also be a fairly trivial change.

andrewmacpherson 4:22 PM
It may come down to what ATAG says. Will file a separate issue about this. Need to review ATAG again.

phenaproxima (he/him) 4:22 PM
++
Keep me posted!

andrewmacpherson 4:22 PM
Configurable would be an option, but documentation will be important. Warnings on the config page, etc.

phenaproxima (he/him) 4:23 PM
Agreed.

Tempted to say critical, this is almost in the area of data loss.

What the heck, we can triage it down again if needs be.

Must decide on policy for this before marking media library as stable.

How is an unintended content change, which happens elsewhere, not data loss?

The title change de-emphasizes the consequences of an action. The problem is not so much that the source of alt text isn't clear when dealing with an instance where a media entity is used. Rather it's that when dealing with a media entity itself, the consequence of changing the alt text isn't conveyed.

It might not be data loss from the perspective of a database administrator, but it is data loss from the perspective of a content manager.

I chatted with @phenaproxima about this...

• It's major, but was still listed as un-triaged on the media_library roadmap. Since we have a feasible proposal for a configurable policy and/or an upgrade path, this issue isn't considered a must-have for #2834729: [META] Roadmap to stabilize Media Library.
• Instead, we agree it's a must-have before enabling the media library in Standard profile.
• It could have a big impact on distros, some of which I expect will enable media library before Standard profile does. That's what change records are for.
• He provided a Google Doc with media library assumptions. I'm going to compare these with the WAI Authoring Tools Accessibilty Guidelines (ATAG) to see if they are harmonious. The ATAG implementation guide has a whole section about "save for re-use" features. Some WCAG criteria are also relevant, notably SC 3.3.4 "Error Prevention (Legal, Financial, Data)" at level AA.

I'll update the media and media_library roadmap issues.