How to get class from widget area

Sidebars are stored in a global variable named $wp_registered_sidebars.

if ( ! function_exists( 'before_sidebar' ) ) {

    function before_sidebar( $columns="five" ) {
        global $wp_registered_sidebars;

        $class_name = $wp_registered_sidebars[$columns]['class'];

        // Apply the markup
        echo "<div id='sidebar' class="$class_name" role="complementary">\n";
    }
}

I assumed that $columns contains the sidebar ID. The value passed into before_sidebar() is the name value given to ‘id' ('id' => 'primary-widget-area') in the arguments. I say that because naming that variable $columns seems strange.