write a joomla function to find the first h2 tag in the content and insert a html content after this tag

function joomla_function( $content ) {
    $content = preg_replace('/(<h2[^>]*>)/', '$1' . '<div class="extra-content">', $content, 1);
    return $content;
}
add_filter( 'the_content', 'joomla_function' );