Add extra Quicktags to WordPress Content box

quicktags.php

<?php 
/* 
* QUICKTAGS
*
* Let's add some extra Quicktags for clients who aren't HTML masters
* They are pretty handy for HTML masters too.
*
* Hook into the 'admin_print_footer_scripts' action
*
*/
add_action( 'admin_print_footer_scripts', 'plate_custom_quicktags' );

function plate_custom_quicktags() {

    if ( wp_script_is( 'quicktags' ) ) { ?>

        <script type="text/javascript">

            QTags.addButton( 'qt-p', 'p', '<p>', '</p>', '', '', 1 );
            QTags.addButton( 'qt-br', 'br', '<br>', '', '', '', 9 );
            QTags.addButton( 'qt-span', 'span', '<span>', '</span>', '', '', 11 );
            QTags.addButton( 'qt-h2', 'h2', '<h2>', '</h2>', '', '', 12 );
            QTags.addButton( 'qt-h3', 'h3', '<h3>', '</h3>', '', '', 13 );
            QTags.addButton( 'qt-h4', 'h4', '<h4>', '</h4>', '', '', 14 );
            QTags.addButton( 'qt-h5', 'h5', '<h5>', '</h5>', '', '', 15 );

        </script>

<?php }

}