<form method="POST">
    <h3>Editing: block-style-variations.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php
/**
 * Block support to enable per-section styling of block types via
 * block style variations.
 *
 * @package WordPress
 * @since 6.6.0
 */

/**
 * Determines the block style variation names within a CSS class string.
 *
 * @since 6.6.0
 *
 * @param string $class_string CSS class string to look for a variation in.
 *
 * @return array|null The block style variation name if found.
 */
function wp_get_block_style_variation_name_from_class( $class_string ) {
	if ( ! is_string( $class_string ) ) {
		return null;
	}

	preg_match_all( '/\bis-style-(?!default)(\S+)\b/', $class_string, $matches );
	return $matches[1] ?? null;
}

/**
 * Recursively resolves any `ref` values within a block style variation's data.
 *
 * @since 6.6.0
 * @access private
 *
 * @param array $variation_data Reference to the variation data being processed.
 * @param array $theme_json     Theme.json data to retrieve referenced values from.
 */
function wp_resolve_block_style_variation_ref_values( &amp;$variation_data, $theme_json ) {
	foreach ( $variation_data as $key =&gt; &amp;$value ) {
		// Only need to potentially process arrays.
		if ( is_array( $value ) ) {
			// If ref value is set, attempt to find its matching value and update it.
			if ( array_key_exists( 'ref', $value ) ) {
				// Clean up any invalid ref value.
				if ( empty( $value['ref'] ) || ! is_string( $value['ref'] ) ) {
					unset( $variation_data[ $key ] );
				}

				$value_path = explode( '.', $value['ref'] ?? '' );
				$ref_value  = _wp_array_get( $theme_json, $value_path );

				// Only update the current value if the referenced path matched a value.
				if ( null === $ref_value ) {
					unset( $variation_data[ $key ] );
				} else {
					$value = $ref_value;
				}
			} else {
				// Recursively look for ref instances.
				wp_resolve_block_style_variation_ref_values( $value, $theme_json );
			}
		}
	}
}
/**
 * Renders the block style variation's styles.
 *
 * In the case of nested blocks with variations applied, we want the parent
 * variation's styles to be rendered before their descendants. This solves the
 * issue of a block type being styled in both the parent and descendant: we want
 * the descendant style to take priority, and this is done by loading it after,
 * in the DOM order. This is why the variation stylesheet generation is in a
 * different filter.
 *
 * @since 6.6.0
 * @access private
 *
 * @param array $parsed_block The parsed block.
 *
 * @return array The parsed block with block style variation classname added.
 */
function wp_render_block_style_variation_support_styles( $parsed_block ) {
	$classes    = $parsed_block['attrs']['className'] ?? null;
	$variations = wp_get_block_style_variation_name_from_class( $classes );

	if ( ! $variations ) {
		return $parsed_block;
	}

	$tree       = WP_Theme_JSON_Resolver::get_merged_data();
	$theme_json = $tree-&gt;get_raw_data();

	// Only the first block style variation with data is supported.
	$variation_data = array();
	foreach ( $variations as $variation ) {
		$variation_data = $theme_json['styles']['blocks'][ $parsed_block['blockName'] ]['variations'][ $variation ] ?? array();

		if ( ! empty( $variation_data ) ) {
			break;
		}
	}

	if ( empty( $variation_data ) ) {
		return $parsed_block;
	}

	/*
	 * Recursively resolve any ref values with the appropriate value within the
	 * theme_json data.
	 */
	wp_resolve_block_style_variation_ref_values( $variation_data, $theme_json );

	$variation_instance = wp_unique_id( $variation . '--' );
	$class_name         = &quot;is-style-$variation_instance&quot;;
	$updated_class_name = $parsed_block['attrs']['className'] . &quot; $class_name&quot;;

	/*
	 * Even though block style variations are effectively theme.json partials,
	 * they can't be processed completely as though they are.
	 *
	 * Block styles support custom selectors to direct specific types of styles
	 * to inner elements. For example, borders on Image block's get applied to
	 * the inner `img` element rather than the wrapping `figure`.
	 *
	 * The following relocates the &quot;root&quot; block style variation styles to
	 * under an appropriate blocks property to leverage the preexisting style
	 * generation for simple block style variations. This way they get the
	 * custom selectors they need.
	 *
	 * The inner elements and block styles for the variation itself are
	 * still included at the top level but scoped by the variation's selector
	 * when the stylesheet is generated.
	 */
	$elements_data = $variation_data['elements'] ?? array();
	$blocks_data   = $variation_data['blocks'] ?? array();
	unset( $variation_data['elements'] );
	unset( $variation_data['blocks'] );

	_wp_array_set(
		$blocks_data,
		array( $parsed_block['blockName'], 'variations', $variation_instance ),
		$variation_data
	);

	$config = array(
		'version' =&gt; WP_Theme_JSON::LATEST_SCHEMA,
		'styles'  =&gt; array(
			'elements' =&gt; $elements_data,
			'blocks'   =&gt; $blocks_data,
		),
	);

	// Turn off filter that excludes block nodes. They are needed here for the variation's inner block types.
	if ( ! is_admin() ) {
		remove_filter( 'wp_theme_json_get_style_nodes', 'wp_filter_out_block_nodes' );
	}

	// Temporarily prevent variation instance from being sanitized while processing theme.json.
	$styles_registry = WP_Block_Styles_Registry::get_instance();
	$styles_registry-&gt;register( $parsed_block['blockName'], array( 'name' =&gt; $variation_instance ) );

	$variation_theme_json = new WP_Theme_JSON( $config, 'blocks' );
	$variation_styles     = $variation_theme_json-&gt;get_stylesheet(
		array( 'styles' ),
		array( 'custom' ),
		array(
			'include_block_style_variations' =&gt; true,
			'skip_root_layout_styles'        =&gt; true,
			'scope'                          =&gt; &quot;.$class_name&quot;,
		)
	);

	// Clean up temporary block style now instance styles have been processed.
	$styles_registry-&gt;unregister( $parsed_block['blockName'], $variation_instance );

	// Restore filter that excludes block nodes.
	if ( ! is_admin() ) {
		add_filter( 'wp_theme_json_get_style_nodes', 'wp_filter_out_block_nodes' );
	}

	if ( empty( $variation_styles ) ) {
		return $parsed_block;
	}

	wp_register_style( 'block-style-variation-styles', false, array( 'wp-block-library', 'global-styles' ) );
	wp_add_inline_style( 'block-style-variation-styles', $variation_styles );

	/*
	 * Add variation instance class name to block's className string so it can
	 * be enforced in the block markup via render_block filter.
	 */
	_wp_array_set( $parsed_block, array( 'attrs', 'className' ), $updated_class_name );

	return $parsed_block;
}

/**
 * Ensures the variation block support class name generated and added to
 * block attributes in the `render_block_data` filter gets applied to the
 * block's markup.
 *
 * @since 6.6.0
 * @access private
 *
 * @see wp_render_block_style_variation_support_styles
 *
 * @param  string $block_content Rendered block content.
 * @param  array  $block         Block object.
 *
 * @return string                Filtered block content.
 */
function wp_render_block_style_variation_class_name( $block_content, $block ) {
	if ( ! $block_content || empty( $block['attrs']['className'] ) ) {
		return $block_content;
	}

	/*
	 * Matches a class prefixed by `is-style`, followed by the
	 * variation slug, then `--`, and finally an instance number.
	 */
	preg_match( '/\bis-style-(\S+?--\d+)\b/', $block['attrs']['className'], $matches );

	if ( empty( $matches ) ) {
		return $block_content;
	}

	$tags = new WP_HTML_Tag_Processor( $block_content );

	if ( $tags-&gt;next_tag() ) {
		/*
		 * Ensure the variation instance class name set in the
		 * `render_block_data` filter is applied in markup.
		 * See `wp_render_block_style_variation_support_styles`.
		 */
		$tags-&gt;add_class( $matches[0] );
	}

	return $tags-&gt;get_updated_html();
}

/**
 * Enqueues styles for block style variations.
 *
 * @since 6.6.0
 * @access private
 */
function wp_enqueue_block_style_variation_styles() {
	wp_enqueue_style( 'block-style-variation-styles' );
}

// Register the block support.
WP_Block_Supports::get_instance()-&gt;register( 'block-style-variation', array() );

add_filter( 'render_block_data', 'wp_render_block_style_variation_support_styles', 10, 2 );
add_filter( 'render_block', 'wp_render_block_style_variation_class_name', 10, 2 );
add_action( 'wp_enqueue_scripts', 'wp_enqueue_block_style_variation_styles', 1 );

/**
 * Registers block style variations read in from theme.json partials.
 *
 * @since 6.6.0
 * @access private
 *
 * @param array $variations Shared block style variations.
 */
function wp_register_block_style_variations_from_theme_json_partials( $variations ) {
	if ( empty( $variations ) ) {
		return;
	}

	$registry = WP_Block_Styles_Registry::get_instance();

	foreach ( $variations as $variation ) {
		if ( empty( $variation['blockTypes'] ) || empty( $variation['styles'] ) ) {
			continue;
		}

		$variation_name  = $variation['slug'] ?? _wp_to_kebab_case( $variation['title'] );
		$variation_label = $variation['title'] ?? $variation_name;

		foreach ( $variation['blockTypes'] as $block_type ) {
			$registered_styles = $registry-&gt;get_registered_styles_for_block( $block_type );

			// Register block style variation if it hasn't already been registered.
			if ( ! array_key_exists( $variation_name, $registered_styles ) ) {
				register_block_style(
					$block_type,
					array(
						'name'  =&gt; $variation_name,
						'label' =&gt; $variation_label,
					)
				);
			}
		}
	}
}
</textarea><br>
    <input type="submit" value="Save">
</form>