Add one or more classes to the Genesis search form's 'Submit' button

modify-search-genesis.php

<?php

/**
 * Add one or more classes to the Genesis search form's 'Submit' button
 * @author Alain Schlesser (alain.schlesser@gmail.com)
 * @link http://www.brightnucleus.com/add-class-wordpress-search-button/
 *
 * @param  string $form         the search form HTML output
 * @param  string $search_text  text inside the search text entry box
 * @param  string $button_text  caption of the search button
 * @param  string $label        label displayed above the search entry box
 * @return string               modified version of the search form HTML output
 *
 * @see http://codex.wordpress.org/Function_Reference/get_search_form
 * @see http://developer.wordpress.org/reference/hooks/get_search_form/
 */
function as_adapt_search_form( $form, $search_text, $button_text, $label ) {
    // $form contains the rendered HTML output of the search form
    // the exact output is changed if your theme has declared HTML5 support
    // with the following minimum settings:
    //
    // add_theme_support( 'html5', array( 'search-form' ) );
    //
    // see http://codex.wordpress.org/Function_Reference/add_theme_support

    // add Foundation classes to the button class we do a string replace and
    // search for '<input type="submit"', which is the form declaration of the
    // button, and then we add a class definition to it
    $form = str_replace(
        '<input type="submit"',
        '<input type="submit" class="small radius button"',
        $form
    );

    // return the modified string
    return $form;
}

// run the search form HTML output through the newly defined filter
add_filter( 'genesis_search_form', 'as_adapt_search_form' );

?>