如何从php for WordPress返回html作为字符串

function play_audio($atts){
    $a = shortcode_atts( array(
        \'url\' => \'\'
    ), $atts );
    wp_enqueue_script(\'player\');
    wp_enqueue_script(\'play_script\');
    wp_enqueue_style(\'progress_bar\');
    return \'<div class="mediPlayer">
    <audio class="listen" preload="none" data-size="250" src=" . $a[url] . "></audio>
</div>
</div>\';
}
add_shortcode( \'playaudio\', \'play_audio\' );