[ON HOLD] [Behind Pref] [Web API] Sanitizer implement namespace handling

[Rumyra]

Acceptance Criteria

• [ ] The listed features are documented sufficiently on MDN
• [ ] BCD is updated
• [ ] Interactive example and data repos are updated if appropriate
• [ ] The content has been reviewed as needed

For folks helping with Firefox related documentation

• [ ] Set bugs to dev-doc-complete
• [ ] Add entry to Firefox release notes if feature is enabled in release
• [ ] Add entry to Firefox experimental features page if feature is not yet enabled in release

Related Gecko bugs

https://bugzilla.mozilla.org/show_bug.cgi?id=1784040

Other

• [ ] Check content open issues to see if any pertain to the subject matter. If there are any that can be closed because of the work, do so. If there are any that can be fixed relatively quickly because of the knowledge from completing this issue and you have time, feel free to go ahead and fix them.
• [ ] Check if glossary updates are required for the feature you're documenting - whether an existing term needs to be updated or a new term should be added.
• [ ] Check if BCD update means that content pages need to have experimental markup removed or deprecated markup added (front matter tags and macros).

[hamishwillee]

Status: On Hold

• This feature generalizes the HTML Sanitizer API, which currently allows you to sanitize HTML elements and attributes, to allow you to specify a namespace in the Sanitizer() constructor. This allows you to sanitize SVG etc if you so wish in the same definition.
• In FF the feature is still behind a preference dom.security.sanitizer.enabled, so this is all hidden.
• The proposal is linked from here https://github.com/WICG/sanitizer-api/issues/181#issuecomment-1403361554

I asked for clarification on stability of this here: https://bugzilla.mozilla.org/show_bug.cgi?id=1784040. The response was that this is too early to document and it is not stable.

So moving to backlog.