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function theme_menu_extras( $menu, $args ) {

	if ( 'primary' !== $args->theme_location )
		return $menu;
	
	ob_start();
    wp_nav_menu(array(
        'theme_location' => 'secondary-menu'
    ) );
    $secmenu = ob_get_clean();
        
        
	$menu  .= '<div class="combine-menu">' . $secmenu . '</div>';
	
	
	return $menu;
}


add_filter( 'wp_nav_menu_items', 'theme_menu_extras', 10, 2 );