Image in collapsed Details block may erroneously get fetchpriority=high even though hidden #76268
Description
Description
This is closely related to the Navigation Overlay issue:
Given a post content that contains two Details block, with an Image block in each:
<!-- wp:details -->
<details class="wp-block-details"><summary>Collapsed kitty</summary><!-- wp:image {"id":415,"sizeSlug":"large","linkDestination":"none"} -->
<figure class="wp-block-image size-large"><img src="http://localhost:8000/wp-content/uploads/2026/03/PXL_20260302_201050363-1024x771.jpg" alt="" class="wp-image-415"/></figure>
<!-- /wp:image --></details>
<!-- /wp:details -->
<!-- wp:details {"showContent":true} -->
<details class="wp-block-details" open><summary>Expanded bison</summary><!-- wp:image {"id":37,"sizeSlug":"large","linkDestination":"none"} -->
<figure class="wp-block-image size-large"><img src="http://localhost:8000/wp-content/uploads/2025/11/Bison_with_its_young-2560w-1024x683.jpg" alt="" class="wp-image-37"/></figure>
<!-- /wp:image --></details>
<!-- /wp:details -->This is rendered by WordPress as follows:
❌ The IMG in the collapsed Details block gets fetchpriority=high even though it is not displayed:
<details class="wp-block-details">
<summary>Collapsed kitty</summary>
<figure class="wp-block-image size-large">
<img
fetchpriority="high"
decoding="async"
width="1024"
height="771"
sizes="(max-width: 645px) 100vw, 645px"
src="http://localhost:8000/wp-content/uploads/2026/03/PXL_20260302_201050363-1024x771.jpg"
alt=""
class="wp-image-415"
srcset="
http://localhost:8000/wp-content/uploads/2026/03/PXL_20260302_201050363-1024x771.jpg 1024w,
http://localhost:8000/wp-content/uploads/2026/03/PXL_20260302_201050363-300x226.jpg 300w,
http://localhost:8000/wp-content/uploads/2026/03/PXL_20260302_201050363-768x578.jpg 768w,
http://localhost:8000/wp-content/uploads/2026/03/PXL_20260302_201050363-1536x1157.jpg 1536w,
http://localhost:8000/wp-content/uploads/2026/03/PXL_20260302_201050363-2048x1542.jpg 2048w
"
/>
</figure>
</details>
<details class="wp-block-details" open>
<summary>Expanded bison</summary>
<figure class="wp-block-image size-large">
<img
decoding="async"
width="1024"
height="683"
sizes="(max-width: 645px) 100vw, 645px"
src="http://localhost:8000/wp-content/uploads/2025/11/Bison_with_its_young-2560w-1024x683.jpg"
alt=""
class="wp-image-37"
srcset="
http://localhost:8000/wp-content/uploads/2025/11/Bison_with_its_young-2560w-1024x683.jpg 1024w,
http://localhost:8000/wp-content/uploads/2025/11/Bison_with_its_young-2560w-300x200.jpg 300w,
http://localhost:8000/wp-content/uploads/2025/11/Bison_with_its_young-2560w-768x512.jpg 768w,
http://localhost:8000/wp-content/uploads/2025/11/Bison_with_its_young-2560w-1536x1025.jpg 1536w,
http://localhost:8000/wp-content/uploads/2025/11/Bison_with_its_young-2560w-2048x1366.jpg 2048w
"
/>
</figure>
</details>Step-by-step reproduction instructions
See above.
Screenshots, screen recording, code snippet
No response
Environment info
- WordPress 7.0-beta3, Gutenberg @ 47e6413
Please confirm that you have searched existing issues in the repo.
- Yes
Please confirm that you have tested with all plugins deactivated except Gutenberg.
- Yes
Please confirm which theme type you used for testing.
- Block
- Classic
- Hybrid (e.g. classic with theme.json)
- Not sure
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