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Source code

function wp_nav_menu( $args = array() ) {

	static $menu_id_slugs = array();



	$defaults = array( 'menu' => '', 'container' => 'div', 'container_class' => '', 'container_id' => '', 'menu_class' => 'menu', 'menu_id' => '',

	'echo' => true, 'fallback_cb' => 'wp_page_menu', 'before' => '', 'after' => '', 'link_before' => '', 'link_after' => '', 'items_wrap' => '<ul id="%1$s" class="%2$s">%3$s</ul>',

	'depth' => 0, 'walker' => '', 'theme_location' => '' );



	$args = wp_parse_args( $args, $defaults );

	$args = apply_filters( 'wp_nav_menu_args', $args );

	$args = (object) $args;



	// Get the nav menu based on the requested menu

	$menu = wp_get_nav_menu_object( $args->menu );



	// Get the nav menu based on the theme_location

	if ( ! $menu && $args->theme_location && ( $locations = get_nav_menu_locations() ) && isset( $locations[ $args->theme_location ] ) )

		$menu = wp_get_nav_menu_object( $locations[ $args->theme_location ] );



	// get the first menu that has items if we still can't find a menu

	if ( ! $menu && !$args->theme_location ) {

		$menus = wp_get_nav_menus();

		foreach ( $menus as $menu_maybe ) {

			if ( $menu_items = wp_get_nav_menu_items($menu_maybe->term_id) ) {

				$menu = $menu_maybe;

				break;

			}

		}

	}



	// If the menu exists, get its items.

	if ( $menu && ! is_wp_error($menu) && !isset($menu_items) )

		$menu_items = wp_get_nav_menu_items( $menu->term_id );



	// If no menu was found or if the menu has no items and no location was requested, call the fallback_cb if it exists

	if ( ( !$menu || is_wp_error($menu) || ( isset($menu_items) && empty($menu_items) && !$args->theme_location ) )

		&& $args->fallback_cb && is_callable( $args->fallback_cb ) )

			return call_user_func( $args->fallback_cb, (array) $args );



	// If no fallback function was specified and the menu doesn't exists, bail.

	if ( !$menu || is_wp_error($menu) )

		return false;



	$nav_menu = $items = '';



	$show_container = false;

	if ( $args->container ) {

		$allowed_tags = apply_filters( 'wp_nav_menu_container_allowedtags', array( 'div', 'nav' ) );

		if ( in_array( $args->container, $allowed_tags ) ) {

			$show_container = true;

			$class = $args->container_class ? ' class="' . esc_attr( $args->container_class ) . '"' : ' class="menu-'. $menu->slug .'-container"';

			$id = $args->container_id ? ' id="' . esc_attr( $args->container_id ) . '"' : '';

			$nav_menu .= '<'. $args->container . $id . $class . '>';

		}

	}



	// Set up the $menu_item variables

	_wp_menu_item_classes_by_context( $menu_items );



	$sorted_menu_items = array();

	foreach ( (array) $menu_items as $key => $menu_item )

		$sorted_menu_items[$menu_item->menu_order] = $menu_item;



	unset($menu_items);



	$sorted_menu_items = apply_filters( 'wp_nav_menu_objects', $sorted_menu_items, $args );



	$items .= walk_nav_menu_tree( $sorted_menu_items, $args->depth, $args );

	unset($sorted_menu_items);



	// Attributes

	if ( ! empty( $args->menu_id ) ) {

		$wrap_id = $args->menu_id;

	} else {

		$wrap_id = 'menu-' . $menu->slug;

		while ( in_array( $wrap_id, $menu_id_slugs ) ) {

			if ( preg_match( '#-(\d+)$#', $wrap_id, $matches ) )

				$wrap_id = preg_replace('#-(\d+)$#', '-' . ++$matches[1], $wrap_id );

			else

				$wrap_id = $wrap_id . '-1';

		}

	}

	$menu_id_slugs[] = $wrap_id;



	$wrap_class = $args->menu_class ? $args->menu_class : '';



	// Allow plugins to hook into the menu to add their own <li>'s

	$items = apply_filters( 'wp_nav_menu_items', $items, $args );

	$items = apply_filters( "wp_nav_menu_{$menu->slug}_items", $items, $args );