wp-bootstrap / wp-bootstrap-navwalker

app/WP_Bootstrap_Navwalker.php

Indentation +535 added lines, -535 removed lines

@@ -42,539 +42,539 @@
  * @param int      $depth  Depth of menu item. Used for padding.
  * @param stdClass $args   An object of wp_nav_menu() arguments.
  */
-    public function start_lvl(&$output, $depth = 0, $args = array())
-    {
-        if (isset($args->item_spacing) && 'discard' === $args->item_spacing) {
-            $t = '';
-            $n = '';
-        } else {
-            $t = "\t";
-            $n = "\n";
-        }
-        $indent = str_repeat($t, $depth);
-        // Default class to add to the file.
-        $classes = array( 'dropdown-menu' );
-        /**
-         * Filters the CSS class(es) applied to a menu list element.
-         *
-         * @since WP 4.8.0
-         *
-         * @param array    $classes The CSS classes that are applied to the menu `<ul>` element.
-         * @param stdClass $args    An object of `wp_nav_menu()` arguments.
-         * @param int      $depth   Depth of menu item. Used for padding.
-         */
-        $class_names = join(' ', apply_filters('nav_menu_submenu_css_class', $classes, $args, $depth));
-        $class_names = $class_names ? ' class="' . esc_attr($class_names) . '"' : '';
-        /**
-         * The `.dropdown-menu` container needs to have a labelledby
-         * attribute which points to it's trigger link.
-         *
-         * Form a string for the labelledby attribute from the the latest
-         * link with an id that was added to the $output.
-         */
-        $labelledby = '';
-        // find all links with an id in the output.
-        preg_match_all('/(<a.*?id=\"|\')(.*?)\"|\'.*?>/im', $output, $matches);
-        // with pointer at end of array check if we got an ID match.
-        if (end($matches[2])) {
-            // build a string to use as aria-labelledby.
-            $labelledby = 'aria-labelledby="' . end($matches[2]) . '"';
-        }
-        $output .= "{$n}{$indent}<ul$class_names $labelledby role=\"menu\">{$n}";
-    }
-
-    /**
-     * Starts the element output.
-     *
-     * @since WP 3.0.0
-     * @since WP 4.4.0 The {@see 'nav_menu_item_args'} filter was added.
-     *
-     * @see Walker_Nav_Menu::start_el()
-     *
-     * @param string   $output Used to append additional content (passed by reference).
-     * @param WP_Post  $item   Menu item data object.
-     * @param int      $depth  Depth of menu item. Used for padding.
-     * @param stdClass $args   An object of wp_nav_menu() arguments.
-     * @param int      $id     Current item ID.
-     */
-
-
-    public function start_el(&$output, $item, $depth = 0, $args = array(), $id = 0)
-    {
-        if (isset($args->item_spacing) && 'discard' === $args->item_spacing) {
-            $t = '';
-            $n = '';
-        } else {
-            $t = "\t";
-            $n = "\n";
-        }
-        $indent = ($depth) ? str_repeat($t, $depth) : '';
-
-        $classes = empty($item->classes) ? array() : (array) $item->classes;
-
-        // Initialize some holder variables to store specially handled item
-        // wrappers and icons.
-        $linkmod_classes = array();
-        $icon_classes    = array();
-
-        /**
-         * Get an updated $classes array without linkmod or icon classes.
-         *
-         * NOTE: linkmod and icon class arrays are passed by reference and
-         * are maybe modified before being used later in this function.
-         */
-        $classes = self::seporate_linkmods_and_icons_from_classes($classes, $linkmod_classes, $icon_classes, $depth);
-
-        // Join any icon classes plucked from $classes into a string.
-        $icon_class_string = join(' ', $icon_classes);
-
-        /**
-         * Filters the arguments for a single nav menu item.
-         *
-         *  WP 4.4.0
-         *
-         * @param stdClass $args  An object of wp_nav_menu() arguments.
-         * @param WP_Post  $item  Menu item data object.
-         * @param int      $depth Depth of menu item. Used for padding.
-         */
-        $args = apply_filters('nav_menu_item_args', $args, $item, $depth);
-
-        // Add .dropdown or .active classes where they are needed.
-        if (isset($args->has_children) && $args->has_children) {
-            $classes[] = 'dropdown';
-        }
-        if (in_array('current-menu-item', $classes, true) || in_array('current-menu-parent', $classes, true)) {
-            $classes[] = 'active';
-        }
-
-        // Add some additional default classes to the item.
-        $classes[] = 'menu-item-' . $item->ID;
-        $classes[] = 'nav-item';
-
-        // Allow filtering the classes.
-        $classes = apply_filters('nav_menu_css_class', array_filter($classes), $item, $args, $depth);
-
-        // Form a string of classes in format: class="class_names".
-        $class_names = join(' ', $classes);
-        $class_names = $class_names ? ' class="' . esc_attr($class_names) . '"' : '';
-
-        /**
-          * Filters the ID applied to a menu item's list item element.
-          *
-          * @since WP 3.0.1
-          * @since WP 4.1.0 The `$depth` parameter was added.
-          *
-          * @param string   $menu_id The ID that is applied to the menu item's `<li>` element.
-          * @param WP_Post  $item    The current menu item.
-          * @param stdClass $args    An object of wp_nav_menu() arguments.
-          * @param int      $depth   Depth of menu item. Used for padding.
-          */
-        $id = apply_filters('nav_menu_item_id', 'menu-item-' . $item->ID, $item, $args, $depth);
-        $id = $id ? ' id="' . esc_attr($id) . '"' : '';
-
-        $output .= $indent . '<li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement"' . $id . $class_names . '>';
-
-        // initialize array for holding the $atts for the link item.
-        $atts = array();
-
-        // Set title from item to the $atts array - if title is empty then
-        // default to item title.
-        if (empty($item->attr_title)) {
-            $atts['title'] = ! empty($item->title) ? strip_tags($item->title) : '';
-        } else {
-            $atts['title'] = $item->attr_title;
-        }
-
-        $atts['target'] = ! empty($item->target) ? $item->target : '';
-        $atts['rel']    = ! empty($item->xfn) ? $item->xfn : '';
-        // If item has_children add atts to <a>.
-        if (isset($args->has_children) && $args->has_children && 0 === $depth && $args->depth > 1) {
-            $atts['href']          = '#';
-            $atts['data-toggle']   = 'dropdown';
-            $atts['aria-haspopup'] = 'true';
-            $atts['aria-expanded'] = 'false';
-            $atts['class']         = 'dropdown-toggle nav-link';
-            $atts['id']            = 'menu-item-dropdown-' . $item->ID;
-        } else {
-            $atts['href'] = ! empty($item->url) ? $item->url : '#';
-            // Items in dropdowns use .dropdown-item instead of .nav-link.
-            if ($depth > 0) {
-                $atts['class'] = 'dropdown-item';
-            } else {
-                $atts['class'] = 'nav-link';
-            }
-        }
-
-        // update atts of this item based on any custom linkmod classes.
-        $atts = self::update_atts_for_linkmod_type($atts, $linkmod_classes);
-        // Allow filtering of the $atts array before using it.
-        $atts = apply_filters('nav_menu_link_attributes', $atts, $item, $args, $depth);
-
-        // Build a string of html containing all the atts for the item.
-        $attributes = '';
-        foreach ($atts as $attr => $value) {
-            if (! empty($value)) {
-                $value       = ('href' === $attr) ? esc_url($value) : esc_attr($value);
-                $attributes .= ' ' . $attr . '="' . $value . '"';
-            }
-        }
-
-        /**
-          * Set a typeflag to easily test if this is a linkmod or not.
-          */
-        $linkmod_type = self::get_linkmod_type($linkmod_classes);
-
-        /**
-          * START appending the internal item contents to the output.
-          */
-        $item_output = isset($args->before) ? $args->before : '';
-        /**
-          * This is the start of the internal nav item. Depending on what
-          * kind of linkmod we have we may need different wrapper elements.
-          */
-        if ('' !== $linkmod_type) {
-            // is linkmod, output the required element opener.
-            $item_output .= self::linkmod_element_open($linkmod_type, $attributes);
-        } else {
-            // With no link mod type set this must be a standard <a> tag.
-            $item_output .= '<a' . $attributes . '>';
-        }
-
-        /**
-          * Initiate empty icon var, then if we have a string containing any
-          * icon classes form the icon markup with an <i> element. This is
-          * output inside of the item before the $title (the link text).
-          */
-        $icon_html = '';
-        if (! empty($icon_class_string)) {
-            // append an <i> with the icon classes to what is output before links.
-            $icon_html = '<i class="' . esc_attr($icon_class_string) . '" aria-hidden="true"></i> ';
-        }
-
-        /** This filter is documented in wp-includes/post-template.php */
-        $title = apply_filters('the_title', $item->title, $item->ID);
-
-        /**
-          * Filters a menu item's title.
-          *
-          * @since WP 4.4.0
-          *
-          * @param string   $title The menu item's title.
-          * @param WP_Post  $item  The current menu item.
-          * @param stdClass $args  An object of wp_nav_menu() arguments.
-          * @param int      $depth Depth of menu item. Used for padding.
-          */
-        $title = apply_filters('nav_menu_item_title', $title, $item, $args, $depth);
-
-        /**
-          * If the .sr-only class was set apply to the nav items text only.
-          */
-        if (in_array('sr-only', $linkmod_classes, true)) {
-            $title         = self::wrap_for_screen_reader($title);
-            $keys_to_unset = array_keys($linkmod_classes, 'sr-only');
-            foreach ($keys_to_unset as $k) {
-                unset($linkmod_classes[ $k ]);
-            }
-        }
-
-        // Put the item contents into $output.
-        $item_output .= isset($args->link_before) ? $args->link_before . $icon_html . $title . $args->link_after : '';
-        /**
-          * This is the end of the internal nav item. We need to close the
-          * correct element depending on the type of link or link mod.
-          */
-        if ('' !== $linkmod_type) {
-            // is linkmod, output the required element opener.
-            $item_output .= self::linkmod_element_close($linkmod_type, $attributes);
-        } else {
-            // With no link mod type set this must be a standard <a> tag.
-            $item_output .= '</a>';
-        }
-
-        $item_output .= isset($args->after) ? $args->after : '';
-
-        /**
-          * END appending the internal item contents to the output.
-          */
-        $output .= apply_filters('walker_nav_menu_start_el', $item_output, $item, $depth, $args);
-    }
-
-
-    /**
-      * Traverse elements to create list from elements.
-      *
-      * Display one element if the element doesn't have any children otherwise,
-      * display the element and its children. Will only traverse up to the max
-      * depth and no ignore elements under that depth. It is possible to set the
-      * max depth to include all depths, see walk() method.
-      *
-      * This method should not be called directly, use the walk() method instead.
-      *
-      * @since WP 2.5.0
-      *
-      * @see Walker::start_lvl()
-      *
-      * @param object $element           Data object.
-      * @param array  $children_elements List of elements to continue traversing (passed by reference).
-      * @param int    $max_depth         Max depth to traverse.
-      * @param int    $depth             Depth of current element.
-      * @param array  $args              An array of arguments.
-      * @param string $output            Used to append additional content (passed by reference).
-      */
-    public function display_element($element, &$children_elements, $max_depth, $depth, $args, &$output)
-    {
-        if (! $element) {
-            return;
-        }
-        $id_field = $this->db_fields['id'];
-        // Display this element.
-        if (is_object($args[0])) {
-            $args[0]->has_children = ! empty($children_elements[ $element->$id_field ]);
-        }
-        parent::display_element($element, $children_elements, $max_depth, $depth, $args, $output);
-    }
-
-
-    /**
-      * Menu Fallback
-      * =============
-      * If this function is assigned to the wp_nav_menu's fallback_cb variable
-      * and a menu has not been assigned to the theme location in the WordPress
-      * menu manager the function with display nothing to a non-logged in user,
-      * and will add a link to the WordPress menu manager if logged in as an admin.
-      *
-      * @param array $args passed from the wp_nav_menu function.
-      */
-    public static function fallback($args)
-    {
-        if (current_user_can('edit_theme_options')) {
-
-        /* Get Arguments. */
-            $container       = $args['container'];
-            $container_id    = $args['container_id'];
-            $container_class = $args['container_class'];
-            $menu_class      = $args['menu_class'];
-            $menu_id         = $args['menu_id'];
-
-            // initialize var to store fallback html.
-            $fallback_output = '';
-
-            if ($container) {
-                $fallback_output .= '<' . esc_attr($container);
-                if ($container_id) {
-                    $fallback_output .= ' id="' . esc_attr($container_id) . '"';
-                }
-                if ($container_class) {
-                    $fallback_output .= ' class="' . esc_attr($container_class) . '"';
-                }
-                $fallback_output .= '>';
-            }
-            $fallback_output .= '<ul';
-            if ($menu_id) {
-                $fallback_output .= ' id="' . esc_attr($menu_id) . '"';
-            }
-            if ($menu_class) {
-                $fallback_output .= ' class="' . esc_attr($menu_class) . '"';
-            }
-            $fallback_output .= '>';
-            $fallback_output .= '<li><a href="' . esc_url(admin_url('nav-menus.php')) . '" title="' . esc_attr__('Add a menu', 'wp-bootstrap-navwalker') . '">' . esc_html__('Add a menu', 'wp-bootstrap-navwalker') . '</a></li>';
-            $fallback_output .= '</ul>';
-            if ($container) {
-                $fallback_output .= '</' . esc_attr($container) . '>';
-            }
-
-            // if $args has 'echo' key and it's true echo, otherwise return.
-            if (array_key_exists('echo', $args) && $args['echo']) {
-                echo $fallback_output; // WPCS: XSS OK.
-            } else {
-                return $fallback_output;
-            }
-        }
-    }
-
-
-    /**
-      * Find any custom linkmod or icon classes and store in their holder
-      * arrays then remove them from the main classes array.
-      *
-      * Supported linkmods: .disabled, .dropdown-header, .dropdown-divider, .sr-only
-      * Supported iconsets: Font Awesome 4/5, Glypicons
-      *
-      * NOTE: This accepts the linkmod and icon arrays by reference.
-      *
-      * @since 4.0.0
-      *
-      * @param array   $classes         an array of classes currently assigned to the item.
-      * @param array   $linkmod_classes an array to hold linkmod classes.
-      * @param array   $icon_classes    an array to hold icon classes.
-      * @param integer $depth           an integer holding current depth level.
-      *
-      * @return array  $classes         a maybe modified array of classnames.
-      */
-    private function seporate_linkmods_and_icons_from_classes($classes, &$linkmod_classes, &$icon_classes, $depth)
-    {
-        // Loop through $classes array to find linkmod or icon classes.
-        foreach ($classes as $key => $class) {
-            // If any special classes are found, store the class in it's
-            // holder array and and unset the item from $classes.
-            if (preg_match('/^disabled|^sr-only/i', $class)) {
-                // Test for .disabled or .sr-only classes.
-                $linkmod_classes[] = $class;
-                unset($classes[ $key ]);
-            } elseif (preg_match('/^dropdown-header|^dropdown-divider|^dropdown-item-text/i', $class) && $depth > 0) {
-                // Test for .dropdown-header or .dropdown-divider and a
-                // depth greater than 0 - IE inside a dropdown.
-                $linkmod_classes[] = $class;
-                unset($classes[ $key ]);
-            } elseif (preg_match('/^fa-(\S*)?|^fa(s|r|l|b)?(\s?)?$/i', $class)) {
-                // Font Awesome.
-                $icon_classes[] = $class;
-                unset($classes[ $key ]);
-            } elseif (preg_match('/^glyphicon-(\S*)?|^glyphicon(\s?)$/i', $class)) {
-                // Glyphicons.
-                $icon_classes[] = $class;
-                unset($classes[ $key ]);
-            }
-        }
-
-        return $classes;
-    }
-
-
-    /**
-      * Return a string containing a linkmod type and update $atts array
-      * accordingly depending on the decided.
-      *
-      * @since 4.0.0
-      *
-      * @param array $linkmod_classes array of any link modifier classes.
-      *
-      * @return string                empty for default, a linkmod type string otherwise.
-      */
-    private function get_linkmod_type($linkmod_classes = array())
-    {
-        $linkmod_type = '';
-        // Loop through array of linkmod classes to handle their $atts.
-        if (! empty($linkmod_classes)) {
-            foreach ($linkmod_classes as $link_class) {
-                if (! empty($link_class)) {
-
-                // check for special class types and set a flag for them.
-                    if ('dropdown-header' === $link_class) {
-                        $linkmod_type = 'dropdown-header';
-                    } elseif ('dropdown-divider' === $link_class) {
-                        $linkmod_type = 'dropdown-divider';
-                    } elseif ('dropdown-item-text' === $link_class) {
-                        $linkmod_type = 'dropdown-item-text';
-                    }
-                }
-            }
-        }
-        return $linkmod_type;
-    }
-
-
-    /**
-      * Update the attributes of a nav item depending on the limkmod classes.
-      *
-      * @since 4.0.0
-      *
-      * @param array $atts            array of atts for the current link in nav item.
-      * @param array $linkmod_classes an array of classes that modify link or nav item behaviors or displays.
-      *
-      * @return array                 maybe updated array of attributes for item.
-      */
-    private function update_atts_for_linkmod_type($atts = array(), $linkmod_classes = array())
-    {
-        if (! empty($linkmod_classes)) {
-            foreach ($linkmod_classes as $link_class) {
-                if (! empty($link_class)) {
-                    // update $atts with a space and the extra classname...
-                    // so long as it's not a sr-only class.
-                    if ('sr-only' !== $link_class) {
-                        $atts['class'] .= ' ' . esc_attr($link_class);
-                    }
-                    // check for special class types we need additional handling for.
-                    if ('disabled' === $link_class) {
-                        // Convert link to '#' and unset open targets.
-                        $atts['href'] = '#';
-                        unset($atts['target']);
-                    } elseif ('dropdown-header' === $link_class || 'dropdown-divider' === $link_class || 'dropdown-item-text' === $link_class) {
-                        // Store a type flag and unset href and target.
-                        unset($atts['href']);
-                        unset($atts['target']);
-                    }
-                }
-            }
-        }
-        return $atts;
-    }
-
-
-    /**
-      * Wraps the passed text in a screen reader only class.
-      *
-      * @since 4.0.0
-      *
-      * @param string $text the string of text to be wrapped in a screen reader class.
-      * @return string      the string wrapped in a span with the class.
-      */
-    private function wrap_for_screen_reader($text = '')
-    {
-        if ($text) {
-            $text = '<span class="sr-only">' . $text . '</span>';
-        }
-        return $text;
-    }
-
-
-    /**
-      * Returns the correct opening element and attributes for a linkmod.
-      *
-      * @since 4.0.0
-      *
-      * @param string $linkmod_type a sting containing a linkmod type flag.
-      * @param string $attributes   a string of attributes to add to the element.
-      *
-      * @return string              a string with the openign tag for the element with attribibutes added.
-      */
-    private function linkmod_element_open($linkmod_type, $attributes = '')
-    {
-        $output = '';
-        if ('dropdown-item-text' === $linkmod_type) {
-            $output .= '<span class="dropdown-item-text"' . $attributes . '>';
-        } elseif ('dropdown-header' === $linkmod_type) {
-            // For a header use a span with the .h6 class instead of a real
-            // header tag so that it doesn't confuse screen readers.
-            $output .= '<span class="dropdown-header h6"' . $attributes . '>';
-        } elseif ('dropdown-divider' === $linkmod_type) {
-            // this is a divider.
-            $output .= '<div class="dropdown-divider"' . $attributes . '>';
-        }
-        return $output;
-    }
-
-
-    /**
-      * Return the correct closing tag for the linkmod element.
-      *
-      * @since 4.0.0
-      *
-      * @param string $linkmod_type a string containing a special linkmod type.
-      *
-      * @return string              a string with the closing tag for this linkmod type.
-      */
-    private function linkmod_element_close($linkmod_type)
-    {
-        $output = '';
-        if ('dropdown-header' === $linkmod_type || 'dropdown-item-text' === $linkmod_type) {
-            // For a header use a span with the .h6 class instead of a real
-            // header tag so that it doesn't confuse screen readers.
-            $output .= '</span>';
-        } elseif ('dropdown-divider' === $linkmod_type) {
-            // this is a divider.
-            $output .= '</div>';
-        }
-        return $output;
-    }
+	public function start_lvl(&$output, $depth = 0, $args = array())
+	{
+		if (isset($args->item_spacing) && 'discard' === $args->item_spacing) {
+			$t = '';
+			$n = '';
+		} else {
+			$t = "\t";
+			$n = "\n";
+		}
+		$indent = str_repeat($t, $depth);
+		// Default class to add to the file.
+		$classes = array( 'dropdown-menu' );
+		/**
+		 * Filters the CSS class(es) applied to a menu list element.
+		 *
+		 * @since WP 4.8.0
+		 *
+		 * @param array    $classes The CSS classes that are applied to the menu `<ul>` element.
+		 * @param stdClass $args    An object of `wp_nav_menu()` arguments.
+		 * @param int      $depth   Depth of menu item. Used for padding.
+		 */
+		$class_names = join(' ', apply_filters('nav_menu_submenu_css_class', $classes, $args, $depth));
+		$class_names = $class_names ? ' class="' . esc_attr($class_names) . '"' : '';
+		/**
+		 * The `.dropdown-menu` container needs to have a labelledby
+		 * attribute which points to it's trigger link.
+		 *
+		 * Form a string for the labelledby attribute from the the latest
+		 * link with an id that was added to the $output.
+		 */
+		$labelledby = '';
+		// find all links with an id in the output.
+		preg_match_all('/(<a.*?id=\"|\')(.*?)\"|\'.*?>/im', $output, $matches);
+		// with pointer at end of array check if we got an ID match.
+		if (end($matches[2])) {
+			// build a string to use as aria-labelledby.
+			$labelledby = 'aria-labelledby="' . end($matches[2]) . '"';
+		}
+		$output .= "{$n}{$indent}<ul$class_names $labelledby role=\"menu\">{$n}";
+	}
+
+	/**
+	 * Starts the element output.
+	 *
+	 * @since WP 3.0.0
+	 * @since WP 4.4.0 The {@see 'nav_menu_item_args'} filter was added.
+	 *
+	 * @see Walker_Nav_Menu::start_el()
+	 *
+	 * @param string   $output Used to append additional content (passed by reference).
+	 * @param WP_Post  $item   Menu item data object.
+	 * @param int      $depth  Depth of menu item. Used for padding.
+	 * @param stdClass $args   An object of wp_nav_menu() arguments.
+	 * @param int      $id     Current item ID.
+	 */
+
+
+	public function start_el(&$output, $item, $depth = 0, $args = array(), $id = 0)
+	{
+		if (isset($args->item_spacing) && 'discard' === $args->item_spacing) {
+			$t = '';
+			$n = '';
+		} else {
+			$t = "\t";
+			$n = "\n";
+		}
+		$indent = ($depth) ? str_repeat($t, $depth) : '';
+
+		$classes = empty($item->classes) ? array() : (array) $item->classes;
+
+		// Initialize some holder variables to store specially handled item
+		// wrappers and icons.
+		$linkmod_classes = array();
+		$icon_classes    = array();
+
+		/**
+		 * Get an updated $classes array without linkmod or icon classes.
+		 *
+		 * NOTE: linkmod and icon class arrays are passed by reference and
+		 * are maybe modified before being used later in this function.
+		 */
+		$classes = self::seporate_linkmods_and_icons_from_classes($classes, $linkmod_classes, $icon_classes, $depth);
+
+		// Join any icon classes plucked from $classes into a string.
+		$icon_class_string = join(' ', $icon_classes);
+
+		/**
+		 * Filters the arguments for a single nav menu item.
+		 *
+		 *  WP 4.4.0
+		 *
+		 * @param stdClass $args  An object of wp_nav_menu() arguments.
+		 * @param WP_Post  $item  Menu item data object.
+		 * @param int      $depth Depth of menu item. Used for padding.
+		 */
+		$args = apply_filters('nav_menu_item_args', $args, $item, $depth);
+
+		// Add .dropdown or .active classes where they are needed.
+		if (isset($args->has_children) && $args->has_children) {
+			$classes[] = 'dropdown';
+		}
+		if (in_array('current-menu-item', $classes, true) || in_array('current-menu-parent', $classes, true)) {
+			$classes[] = 'active';
+		}
+
+		// Add some additional default classes to the item.
+		$classes[] = 'menu-item-' . $item->ID;
+		$classes[] = 'nav-item';
+
+		// Allow filtering the classes.
+		$classes = apply_filters('nav_menu_css_class', array_filter($classes), $item, $args, $depth);
+
+		// Form a string of classes in format: class="class_names".
+		$class_names = join(' ', $classes);
+		$class_names = $class_names ? ' class="' . esc_attr($class_names) . '"' : '';
+
+		/**
+		 * Filters the ID applied to a menu item's list item element.
+		 *
+		 * @since WP 3.0.1
+		 * @since WP 4.1.0 The `$depth` parameter was added.
+		 *
+		 * @param string   $menu_id The ID that is applied to the menu item's `<li>` element.
+		 * @param WP_Post  $item    The current menu item.
+		 * @param stdClass $args    An object of wp_nav_menu() arguments.
+		 * @param int      $depth   Depth of menu item. Used for padding.
+		 */
+		$id = apply_filters('nav_menu_item_id', 'menu-item-' . $item->ID, $item, $args, $depth);
+		$id = $id ? ' id="' . esc_attr($id) . '"' : '';
+
+		$output .= $indent . '<li itemscope="itemscope" itemtype="https://www.schema.org/SiteNavigationElement"' . $id . $class_names . '>';
+
+		// initialize array for holding the $atts for the link item.
+		$atts = array();
+
+		// Set title from item to the $atts array - if title is empty then
+		// default to item title.
+		if (empty($item->attr_title)) {
+			$atts['title'] = ! empty($item->title) ? strip_tags($item->title) : '';
+		} else {
+			$atts['title'] = $item->attr_title;
+		}
+
+		$atts['target'] = ! empty($item->target) ? $item->target : '';
+		$atts['rel']    = ! empty($item->xfn) ? $item->xfn : '';
+		// If item has_children add atts to <a>.
+		if (isset($args->has_children) && $args->has_children && 0 === $depth && $args->depth > 1) {
+			$atts['href']          = '#';
+			$atts['data-toggle']   = 'dropdown';
+			$atts['aria-haspopup'] = 'true';
+			$atts['aria-expanded'] = 'false';
+			$atts['class']         = 'dropdown-toggle nav-link';
+			$atts['id']            = 'menu-item-dropdown-' . $item->ID;
+		} else {
+			$atts['href'] = ! empty($item->url) ? $item->url : '#';
+			// Items in dropdowns use .dropdown-item instead of .nav-link.
+			if ($depth > 0) {
+				$atts['class'] = 'dropdown-item';
+			} else {
+				$atts['class'] = 'nav-link';
+			}
+		}
+
+		// update atts of this item based on any custom linkmod classes.
+		$atts = self::update_atts_for_linkmod_type($atts, $linkmod_classes);
+		// Allow filtering of the $atts array before using it.
+		$atts = apply_filters('nav_menu_link_attributes', $atts, $item, $args, $depth);
+
+		// Build a string of html containing all the atts for the item.
+		$attributes = '';
+		foreach ($atts as $attr => $value) {
+			if (! empty($value)) {
+				$value       = ('href' === $attr) ? esc_url($value) : esc_attr($value);
+				$attributes .= ' ' . $attr . '="' . $value . '"';
+			}
+		}
+
+		/**
+		 * Set a typeflag to easily test if this is a linkmod or not.
+		 */
+		$linkmod_type = self::get_linkmod_type($linkmod_classes);
+
+		/**
+		 * START appending the internal item contents to the output.
+		 */
+		$item_output = isset($args->before) ? $args->before : '';
+		/**
+		 * This is the start of the internal nav item. Depending on what
+		 * kind of linkmod we have we may need different wrapper elements.
+		 */
+		if ('' !== $linkmod_type) {
+			// is linkmod, output the required element opener.
+			$item_output .= self::linkmod_element_open($linkmod_type, $attributes);
+		} else {
+			// With no link mod type set this must be a standard <a> tag.
+			$item_output .= '<a' . $attributes . '>';
+		}
+
+		/**
+		 * Initiate empty icon var, then if we have a string containing any
+		 * icon classes form the icon markup with an <i> element. This is
+		 * output inside of the item before the $title (the link text).
+		 */
+		$icon_html = '';
+		if (! empty($icon_class_string)) {
+			// append an <i> with the icon classes to what is output before links.
+			$icon_html = '<i class="' . esc_attr($icon_class_string) . '" aria-hidden="true"></i> ';
+		}
+
+		/** This filter is documented in wp-includes/post-template.php */
+		$title = apply_filters('the_title', $item->title, $item->ID);
+
+		/**
+		 * Filters a menu item's title.
+		 *
+		 * @since WP 4.4.0
+		 *
+		 * @param string   $title The menu item's title.
+		 * @param WP_Post  $item  The current menu item.
+		 * @param stdClass $args  An object of wp_nav_menu() arguments.
+		 * @param int      $depth Depth of menu item. Used for padding.
+		 */
+		$title = apply_filters('nav_menu_item_title', $title, $item, $args, $depth);
+
+		/**
+		 * If the .sr-only class was set apply to the nav items text only.
+		 */
+		if (in_array('sr-only', $linkmod_classes, true)) {
+			$title         = self::wrap_for_screen_reader($title);
+			$keys_to_unset = array_keys($linkmod_classes, 'sr-only');
+			foreach ($keys_to_unset as $k) {
+				unset($linkmod_classes[ $k ]);
+			}
+		}
+
+		// Put the item contents into $output.
+		$item_output .= isset($args->link_before) ? $args->link_before . $icon_html . $title . $args->link_after : '';
+		/**
+		 * This is the end of the internal nav item. We need to close the
+		 * correct element depending on the type of link or link mod.
+		 */
+		if ('' !== $linkmod_type) {
+			// is linkmod, output the required element opener.
+			$item_output .= self::linkmod_element_close($linkmod_type, $attributes);
+		} else {
+			// With no link mod type set this must be a standard <a> tag.
+			$item_output .= '</a>';
+		}
+
+		$item_output .= isset($args->after) ? $args->after : '';
+
+		/**
+		 * END appending the internal item contents to the output.
+		 */
+		$output .= apply_filters('walker_nav_menu_start_el', $item_output, $item, $depth, $args);
+	}
+
+
+	/**
+	 * Traverse elements to create list from elements.
+	 *
+	 * Display one element if the element doesn't have any children otherwise,
+	 * display the element and its children. Will only traverse up to the max
+	 * depth and no ignore elements under that depth. It is possible to set the
+	 * max depth to include all depths, see walk() method.
+	 *
+	 * This method should not be called directly, use the walk() method instead.
+	 *
+	 * @since WP 2.5.0
+	 *
+	 * @see Walker::start_lvl()
+	 *
+	 * @param object $element           Data object.
+	 * @param array  $children_elements List of elements to continue traversing (passed by reference).
+	 * @param int    $max_depth         Max depth to traverse.
+	 * @param int    $depth             Depth of current element.
+	 * @param array  $args              An array of arguments.
+	 * @param string $output            Used to append additional content (passed by reference).
+	 */
+	public function display_element($element, &$children_elements, $max_depth, $depth, $args, &$output)
+	{
+		if (! $element) {
+			return;
+		}
+		$id_field = $this->db_fields['id'];
+		// Display this element.
+		if (is_object($args[0])) {
+			$args[0]->has_children = ! empty($children_elements[ $element->$id_field ]);
+		}
+		parent::display_element($element, $children_elements, $max_depth, $depth, $args, $output);
+	}
+
+
+	/**
+	 * Menu Fallback
+	 * =============
+	 * If this function is assigned to the wp_nav_menu's fallback_cb variable
+	 * and a menu has not been assigned to the theme location in the WordPress
+	 * menu manager the function with display nothing to a non-logged in user,
+	 * and will add a link to the WordPress menu manager if logged in as an admin.
+	 *
+	 * @param array $args passed from the wp_nav_menu function.
+	 */
+	public static function fallback($args)
+	{
+		if (current_user_can('edit_theme_options')) {
+
+		/* Get Arguments. */
+			$container       = $args['container'];
+			$container_id    = $args['container_id'];
+			$container_class = $args['container_class'];
+			$menu_class      = $args['menu_class'];
+			$menu_id         = $args['menu_id'];
+
+			// initialize var to store fallback html.
+			$fallback_output = '';
+
+			if ($container) {
+				$fallback_output .= '<' . esc_attr($container);
+				if ($container_id) {
+					$fallback_output .= ' id="' . esc_attr($container_id) . '"';
+				}
+				if ($container_class) {
+					$fallback_output .= ' class="' . esc_attr($container_class) . '"';
+				}
+				$fallback_output .= '>';
+			}
+			$fallback_output .= '<ul';
+			if ($menu_id) {
+				$fallback_output .= ' id="' . esc_attr($menu_id) . '"';
+			}
+			if ($menu_class) {
+				$fallback_output .= ' class="' . esc_attr($menu_class) . '"';
+			}
+			$fallback_output .= '>';
+			$fallback_output .= '<li><a href="' . esc_url(admin_url('nav-menus.php')) . '" title="' . esc_attr__('Add a menu', 'wp-bootstrap-navwalker') . '">' . esc_html__('Add a menu', 'wp-bootstrap-navwalker') . '</a></li>';
+			$fallback_output .= '</ul>';
+			if ($container) {
+				$fallback_output .= '</' . esc_attr($container) . '>';
+			}
+
+			// if $args has 'echo' key and it's true echo, otherwise return.
+			if (array_key_exists('echo', $args) && $args['echo']) {
+				echo $fallback_output; // WPCS: XSS OK.
+			} else {
+				return $fallback_output;
+			}
+		}
+	}
+
+
+	/**
+	 * Find any custom linkmod or icon classes and store in their holder
+	 * arrays then remove them from the main classes array.
+	 *
+	 * Supported linkmods: .disabled, .dropdown-header, .dropdown-divider, .sr-only
+	 * Supported iconsets: Font Awesome 4/5, Glypicons
+	 *
+	 * NOTE: This accepts the linkmod and icon arrays by reference.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param array   $classes         an array of classes currently assigned to the item.
+	 * @param array   $linkmod_classes an array to hold linkmod classes.
+	 * @param array   $icon_classes    an array to hold icon classes.
+	 * @param integer $depth           an integer holding current depth level.
+	 *
+	 * @return array  $classes         a maybe modified array of classnames.
+	 */
+	private function seporate_linkmods_and_icons_from_classes($classes, &$linkmod_classes, &$icon_classes, $depth)
+	{
+		// Loop through $classes array to find linkmod or icon classes.
+		foreach ($classes as $key => $class) {
+			// If any special classes are found, store the class in it's
+			// holder array and and unset the item from $classes.
+			if (preg_match('/^disabled|^sr-only/i', $class)) {
+				// Test for .disabled or .sr-only classes.
+				$linkmod_classes[] = $class;
+				unset($classes[ $key ]);
+			} elseif (preg_match('/^dropdown-header|^dropdown-divider|^dropdown-item-text/i', $class) && $depth > 0) {
+				// Test for .dropdown-header or .dropdown-divider and a
+				// depth greater than 0 - IE inside a dropdown.
+				$linkmod_classes[] = $class;
+				unset($classes[ $key ]);
+			} elseif (preg_match('/^fa-(\S*)?|^fa(s|r|l|b)?(\s?)?$/i', $class)) {
+				// Font Awesome.
+				$icon_classes[] = $class;
+				unset($classes[ $key ]);
+			} elseif (preg_match('/^glyphicon-(\S*)?|^glyphicon(\s?)$/i', $class)) {
+				// Glyphicons.
+				$icon_classes[] = $class;
+				unset($classes[ $key ]);
+			}
+		}
+
+		return $classes;
+	}
+
+
+	/**
+	 * Return a string containing a linkmod type and update $atts array
+	 * accordingly depending on the decided.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param array $linkmod_classes array of any link modifier classes.
+	 *
+	 * @return string                empty for default, a linkmod type string otherwise.
+	 */
+	private function get_linkmod_type($linkmod_classes = array())
+	{
+		$linkmod_type = '';
+		// Loop through array of linkmod classes to handle their $atts.
+		if (! empty($linkmod_classes)) {
+			foreach ($linkmod_classes as $link_class) {
+				if (! empty($link_class)) {
+
+				// check for special class types and set a flag for them.
+					if ('dropdown-header' === $link_class) {
+						$linkmod_type = 'dropdown-header';
+					} elseif ('dropdown-divider' === $link_class) {
+						$linkmod_type = 'dropdown-divider';
+					} elseif ('dropdown-item-text' === $link_class) {
+						$linkmod_type = 'dropdown-item-text';
+					}
+				}
+			}
+		}
+		return $linkmod_type;
+	}
+
+
+	/**
+	 * Update the attributes of a nav item depending on the limkmod classes.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param array $atts            array of atts for the current link in nav item.
+	 * @param array $linkmod_classes an array of classes that modify link or nav item behaviors or displays.
+	 *
+	 * @return array                 maybe updated array of attributes for item.
+	 */
+	private function update_atts_for_linkmod_type($atts = array(), $linkmod_classes = array())
+	{
+		if (! empty($linkmod_classes)) {
+			foreach ($linkmod_classes as $link_class) {
+				if (! empty($link_class)) {
+					// update $atts with a space and the extra classname...
+					// so long as it's not a sr-only class.
+					if ('sr-only' !== $link_class) {
+						$atts['class'] .= ' ' . esc_attr($link_class);
+					}
+					// check for special class types we need additional handling for.
+					if ('disabled' === $link_class) {
+						// Convert link to '#' and unset open targets.
+						$atts['href'] = '#';
+						unset($atts['target']);
+					} elseif ('dropdown-header' === $link_class || 'dropdown-divider' === $link_class || 'dropdown-item-text' === $link_class) {
+						// Store a type flag and unset href and target.
+						unset($atts['href']);
+						unset($atts['target']);
+					}
+				}
+			}
+		}
+		return $atts;
+	}
+
+
+	/**
+	 * Wraps the passed text in a screen reader only class.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $text the string of text to be wrapped in a screen reader class.
+	 * @return string      the string wrapped in a span with the class.
+	 */
+	private function wrap_for_screen_reader($text = '')
+	{
+		if ($text) {
+			$text = '<span class="sr-only">' . $text . '</span>';
+		}
+		return $text;
+	}
+
+
+	/**
+	 * Returns the correct opening element and attributes for a linkmod.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $linkmod_type a sting containing a linkmod type flag.
+	 * @param string $attributes   a string of attributes to add to the element.
+	 *
+	 * @return string              a string with the openign tag for the element with attribibutes added.
+	 */
+	private function linkmod_element_open($linkmod_type, $attributes = '')
+	{
+		$output = '';
+		if ('dropdown-item-text' === $linkmod_type) {
+			$output .= '<span class="dropdown-item-text"' . $attributes . '>';
+		} elseif ('dropdown-header' === $linkmod_type) {
+			// For a header use a span with the .h6 class instead of a real
+			// header tag so that it doesn't confuse screen readers.
+			$output .= '<span class="dropdown-header h6"' . $attributes . '>';
+		} elseif ('dropdown-divider' === $linkmod_type) {
+			// this is a divider.
+			$output .= '<div class="dropdown-divider"' . $attributes . '>';
+		}
+		return $output;
+	}
+
+
+	/**
+	 * Return the correct closing tag for the linkmod element.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $linkmod_type a string containing a special linkmod type.
+	 *
+	 * @return string              a string with the closing tag for this linkmod type.
+	 */
+	private function linkmod_element_close($linkmod_type)
+	{
+		$output = '';
+		if ('dropdown-header' === $linkmod_type || 'dropdown-item-text' === $linkmod_type) {
+			// For a header use a span with the .h6 class instead of a real
+			// header tag so that it doesn't confuse screen readers.
+			$output .= '</span>';
+		} elseif ('dropdown-divider' === $linkmod_type) {
+			// this is a divider.
+			$output .= '</div>';
+		}
+		return $output;
+	}
 }