Block visibility supports: implement block visibility based on breakpoints

[ramonjd]

Note

The feature is still in an experiment in Gutenberg, so this PR is a placeholder for stabilization. See: WordPress/gutenberg#73994

This PR syncs the changes in WordPress/gutenberg#73994. It:

• implements breakpoint visibility support in block rendering, allowing blocks to be hidden or shown based on defined breakpoints.
• introduces the display property to the safecss_filter_attr function.

Unit tests:

npm run test:php -- --filter Tests_Kses 
npm run test:php -- --filter Tests_Block_Supports_Block_Visibility

To test manually, enable the experiment:

Then copy and paste this into your post editor, publish and view the frontend.

<!-- wp:paragraph {"metadata":{"blockVisibility":{"mobile":false}}} -->
<p>🔴 Hidden on MOBILE (≤599px) - You should see this on tablet and desktop only</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"metadata":{"blockVisibility":{"tablet":false}}} -->
<p>🟡 Hidden on TABLET (600-959px) - You should see this on mobile and desktop only</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"metadata":{"blockVisibility":{"desktop":false}}} -->
<p>🟢 Hidden on DESKTOP (≥960px) - You should see this on mobile and tablet only</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"metadata":{"blockVisibility":{"mobile":false,"desktop":false}}} -->
<p>🟣 Hidden on MOBILE and DESKTOP - You should only see this on tablet (600-959px)</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"metadata":{"blockVisibility":{"mobile":false,"tablet":false}}} -->
<p>🔵 Hidden on MOBILE and TABLET - You should only see this on desktop (≥960px)</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"metadata":{"blockVisibility":{"tablet":false,"desktop":false}}} -->
<p>🟠 Hidden on TABLET and DESKTOP - You should only see this on mobile (≤599px)</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"metadata":{"blockVisibility":{"mobile":true,"tablet":true,"desktop":true}}} -->
<p>✅ Visible on ALL breakpoints - You should always see this</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"metadata":{"blockVisibility":false}} -->
<p>❌ Completely HIDDEN (boolean false) - You should never see this</p>
<!-- /wp:paragraph -->

Kapture.2025-12-14.at.19.37.29.mp4

Make sure to test with the experiment off as well. The last item should never show with the experiment on and off.

Trac ticket: https://core.trac.wordpress.org/ticket/64414

[github-actions]

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Props ramonopoly.

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[github-actions]

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