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Block Visibility: Add fetchpriority=auto to IMG tags in blocks with conditional viewport visibility to prevent potential erroneous high loading priority #76302

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Merged
westonruter merged 4 commits into from
Mar 9, 2026
Merged

Block Visibility: Add fetchpriority=auto to IMG tags in blocks with conditional viewport visibility to prevent potential erroneous high loading priority #76302

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ed4e1b0
Add fetchpriority=low to IMG tags in blocks with conditional viewport…
westonruter Mar 9, 2026
7f663c3
Add backport changelog
westonruter Mar 9, 2026
fa0522f
Reuse HTML Tag Processor
westonruter Mar 9, 2026
6fedb39
Use affect instead of effect
westonruter Mar 9, 2026
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3 changes: 3 additions & 0 deletions backport-changelog/7.0/11196.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
https://github.com/WordPress/wordpress-develop/pull/11196

* https://github.com/WordPress/gutenberg/pull/76302
10 changes: 10 additions & 0 deletions lib/block-supports/block-visibility.php
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Expand Up @@ -137,6 +137,16 @@ function gutenberg_render_block_visibility_support( $block_content, $block ) {
$processor = new WP_HTML_Tag_Processor( $block_content );
if ( $processor->next_tag() ) {
$processor->add_class( implode( ' ', $class_names ) );

/*
* Set all IMG tags to be `fetchpriority=auto` so that wp_get_loading_optimization_attributes() won't add
* `fetchpriority=high` or increment the media count to affect whether subsequent IMG tags get `loading=lazy`.
*/
do {
if ( 'IMG' === $processor->get_tag() ) {
$processor->set_attribute( 'fetchpriority', 'auto' );

@mukeshpanchal27 mukeshpanchal27 Mar 9, 2026

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Question: If an image already had fetchpriority="high" (or low), this will overwrite it, which could be a regression for intentionally prioritized LCP images.

Even though If we set to "auto", this is still a global mutation of all images inside the block HTML.

@westonruter westonruter Mar 9, 2026

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If the image intentionally had fetchpriority="high" then this still would have been wrong, correct? It is highly unlikely that the block would be intentionally adding this while also being aware that it is in a viewport-conditional block.

}
} while ( $processor->next_tag() );
Comment on lines +141 to +149

@westonruter westonruter Mar 9, 2026

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Test case included in core PR: https://github.com/WordPress/wordpress-develop/pull/11196/changes#diff-643478eb4a42b141594dcd64723813a6255c6381e7aa6a30b4d4ac414d1271d1

$block_content = $processor->get_updated_html();
}
}
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