<?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' ); 
 
 |