wp-includes/media.php:2179Checks whether the given 'sizes' attribute includes the 'auto' keyword as the first item in the list.
$sizes_attrstringboolfunction wp_sizes_attribute_includes_valid_auto( string $sizes_attr ): bool { list( $first_size ) = explode( ',', $sizes_attr, 2 ); return 'auto' === strtolower( trim( $first_size, " \t\f\r\n" ) );}Introduced in 6.7.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/media.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.