diff -r 7b1b88e27a20 -r 48c4eec2b7e6 wp/wp-includes/blocks/heading.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/blocks/heading.php	Fri Sep 05 18:40:08 2025 +0200
@@ -0,0 +1,56 @@
+<?php
+/**
+ * Appending the wp-block-heading to before rendering the stored `core/heading` block contents.
+ *
+ * @package WordPress
+ */
+
+/**
+ * Adds a wp-block-heading class to the heading block content.
+ *
+ * For example, the following block content:
+ *  <h2 class="align-left">Hello World</h2>
+ *
+ * Would be transformed to:
+ *  <h2 class="align-left wp-block-heading">Hello World</h2>
+ *
+ * @since 6.2.0
+ *
+ * @param array  $attributes Attributes of the block being rendered.
+ * @param string $content Content of the block being rendered.
+ *
+ * @return string The content of the block being rendered.
+ */
+function block_core_heading_render( $attributes, $content ) {
+	if ( ! $content ) {
+		return $content;
+	}
+
+	$p = new WP_HTML_Tag_Processor( $content );
+
+	$header_tags = array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' );
+	while ( $p->next_tag() ) {
+		if ( in_array( $p->get_tag(), $header_tags, true ) ) {
+			$p->add_class( 'wp-block-heading' );
+			break;
+		}
+	}
+
+	return $p->get_updated_html();
+}
+
+/**
+ * Registers the `core/heading` block on server.
+ *
+ * @since 6.2.0
+ */
+function register_block_core_heading() {
+	register_block_type_from_metadata(
+		__DIR__ . '/heading',
+		array(
+			'render_callback' => 'block_core_heading_render',
+		)
+	);
+}
+
+add_action( 'init', 'register_block_core_heading' );