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<?php
//* Do NOT include the opening php tag shown above. Copy the code shown below.
add_filter( 'wp_nav_menu_items', 'theme_menu_extras', 10, 2 );
/**
 * Filter menu items, appending either a search form or today's date.
 *
 * @param string   $menu HTML string of list items.
 * @param stdClass $args Menu arguments.
 *
 * @return string Amended HTML string of list items.
 */
function theme_menu_extras( $menu, $args ) {
	//* Change 'primary' to 'secondary' to add extras to the secondary navigation menu
	if ( 'primary' !== $args->theme_location )
		return $menu;
	//* Uncomment this block to add a search form to the navigation menu
	/*
	ob_start();
	get_search_form();
	$search = ob_get_clean();
	$menu  .= '<li class="right search">' . $search . '</li>';
	*/
	//* Uncomment this block to add the date to the navigation menu
	/*
	$menu .= '<li class="right date">' . date_i18n( get_option( 'date_format' ) ) . '</li>';
	*/
	return $menu;
}

//source http://my.studiopress.com/snippets/nav-extras/