wp-includes/block-supports/custom-classname.php:17Registers the custom classname block attribute for block types that support it.
$block_typeWP_Block_Typefunction wp_register_custom_classname_support( $block_type ) { $has_custom_classname_support = block_has_support( $block_type, 'customClassName', true ); if ( $has_custom_classname_support ) { if ( ! $block_type->attributes ) { $block_type->attributes = array(); } if ( ! array_key_exists( 'className', $block_type->attributes ) ) { $block_type->attributes['className'] = array( 'type' => 'string', ); } }}Introduced in 5.6.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/block-supports/custom-classname.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.