[QTI] Cannot publish a channel because of an exercise containing strikethrough formatted text

[pcenov]

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Observed behavior

Similarly to #5895 it's not possible to publish the following test channel containing an exercise with a question containing strikethrough formatting of the text: <s>test</>. This issue is not happening on production. No errors in the browser console:

strikethrough.mp4

Expected behavior

Formatted text should not impact the publishing of a channel.

Steps to reproduce the issue

1. Sign in to Studio at unstable
2. Go to Channel > Channel editor > New exercise
3. Create an exercise containing strikethrough formatting of the text
4. Attempt to publish the channel

Usage Details

• Studio Unstable
• OS: Windows 11
• Browser: Chrome, Firefox

[pcenov]

@radinamatic @AlexVelezLl

[radinamatic]

This is reoccurrence, should have been fixed in #5595

[AlexVelezLl]

No, this is a new issue, it's because of the new QTI publish workflow https://learningequality.sentry.io/issues/7735455836/?environment=unstable&project=1252819&query=is%3Aunresolved&referrer=issue-stream.

[AlexVelezLl]

This issue is because the QTI 3.0 specs do not allow <s> or <del> tags, and our QTI bundling workflow bans them at publish time. To still support the strikethrough button, we will use the style attribute on a <span> tag instead. style isn't defined in the QTI 3.0 XSD either, but at least this does not cause any validation errors.

For this, we will need to refactor code from https://github.com/learningequality/studio/pull/6073/changes#diff-48a08c8b3283d25275c3a266a3c25dda576f0d131965a2739729f68227bb1eeeR89 to allow converting these tags into span tags with style attributes rather than just stripping them. We'll also need to update the Rich Text Editor in Studio to recognize the proper style rules for active strikethrough and update the toolbar buttons to toggle it.

We should do the same for the underline button, since <u> isn't valid in QTI 3.0 either. And now that we're going in this direction, we can also show the text alignment buttons again.

On the Kolibri side, the style attribute is currently supported (learningequality/kolibri#14984); however, there is an allowlist that should be updated accordingly. Before merging the PR for this, follow-up issues/PRs should be opened there to update the allowlist.