diff -r 7b1b88e27a20 -r 48c4eec2b7e6 wp/wp-includes/block-supports/shadow.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/block-supports/shadow.php	Fri Sep 05 18:40:08 2025 +0200
@@ -0,0 +1,85 @@
+<?php
+/**
+ * Shadow block support flag.
+ *
+ * @package WordPress
+ * @since 6.3.0
+ */
+
+/**
+ * Registers the style and shadow block attributes for block types that support it.
+ *
+ * @since 6.3.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type Block Type.
+ */
+function wp_register_shadow_support( $block_type ) {
+	$has_shadow_support = block_has_support( $block_type, 'shadow', false );
+
+	if ( ! $has_shadow_support ) {
+		return;
+	}
+
+	if ( ! $block_type->attributes ) {
+		$block_type->attributes = array();
+	}
+
+	if ( array_key_exists( 'style', $block_type->attributes ) ) {
+		$block_type->attributes['style'] = array(
+			'type' => 'object',
+		);
+	}
+
+	if ( array_key_exists( 'shadow', $block_type->attributes ) ) {
+		$block_type->attributes['shadow'] = array(
+			'type' => 'string',
+		);
+	}
+}
+
+/**
+ * Add CSS classes and inline styles for shadow features to the incoming attributes array.
+ * This will be applied to the block markup in the front-end.
+ *
+ * @since 6.3.0
+ * @since 6.6.0 Return early if __experimentalSkipSerialization is true.
+ * @access private
+ *
+ * @param  WP_Block_Type $block_type       Block type.
+ * @param  array         $block_attributes Block attributes.
+ * @return array Shadow CSS classes and inline styles.
+ */
+function wp_apply_shadow_support( $block_type, $block_attributes ) {
+	$has_shadow_support = block_has_support( $block_type, 'shadow', false );
+
+	if (
+		! $has_shadow_support ||
+		wp_should_skip_block_supports_serialization( $block_type, 'shadow' )
+	) {
+		return array();
+	}
+
+	$shadow_block_styles = array();
+
+	$custom_shadow                 = $block_attributes['style']['shadow'] ?? null;
+	$shadow_block_styles['shadow'] = $custom_shadow;
+
+	$attributes = array();
+	$styles     = wp_style_engine_get_styles( $shadow_block_styles );
+
+	if ( ! empty( $styles['css'] ) ) {
+		$attributes['style'] = $styles['css'];
+	}
+
+	return $attributes;
+}
+
+// Register the block support.
+WP_Block_Supports::get_instance()->register(
+	'shadow',
+	array(
+		'register_attribute' => 'wp_register_shadow_support',
+		'apply'              => 'wp_apply_shadow_support',
+	)
+);