Allow hidden="until-found"

[chefarbeiter]

Description

The default rule for [hidden] in Reboot (see Docs) prevents the usage of the hidden=until-found feature of browsers. This PR excludes elements with hidden=until-found from the reboot rule.

Motivation & Context

I want to use the hidden=until-found feature for an application in which I use Bootstrap, but I can't because of the current reboot rule.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-42025--twbs-bootstrap.netlify.app

Related issues

#40688

Test

I'm using the following minimal sample for testing:

<h1>Hidden until-found</h1>
<div>I'm always visible</div>
<div hidden="until-found">Search for me</div>
<div hidden>I'm always hidden</div>
<div>I'm always visible</div>

When I search for “Search” in the browser before the fix, the text is not found and displayed:

With the fix, the element with hidden=until-found is displayed. As before, the element with hidden is generally not visible: