Focus Manager Node Plugin: Accessible TabView
This example illustrates how to create an accessible tabview widget using the Focus Manager Node Plugin, Event's delegation support, and Node's support for the WAI-ARIA Roles and States.
Today's News
Top Stories
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Officer stopped suspect on day of Ariz. shooting (AP)
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Obama to be nation's consoler at memorial service (AP)
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Winter storm buries southern New England (AP)
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Riots reach Tunisia's capital, curfew imposed (AP)
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Torrential rain, mudslides in Brazil kill 140 (AP)
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Palin: Journalists incite hatred after AZ shooting (AP)
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US military chief: Enemy in Afghanistan is losing (AP)
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Gov. Quinn promises to quickly sign Ill. tax hike (AP)
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Aretha Franklin says her health is 'superb' (AP)
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Latest German animal star a cross-eyed opossum (AP)
World News
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Hezbollah and allies resign, toppling Lebanon government (Reuters)
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Haitians remember 2010 quake, seek way out of 'hell' (Reuters)
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At least 127 dead as rains pummel Brazil regions (Reuters)
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Suicide bomber kills 17 police and soldiers in Pakistan (Reuters)
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Gaza militants say to halt rocket fire at Israel (Reuters)
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Lebanon Government Collapse: Hizballah Exits Cabinet (Time.com)
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Stocks head higher as worries about Europe ease (AP)
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Hezbollah and its allies topple Lebanon government (AP)
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Torrential rain, mudslides in Brazil kill 140 (AP)
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Religion and region at play in Nigerian election (AP)
Entertainment News
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`Green Hornet' actor Eddie Furlong arrested (AP)
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Oscar winners Gibney, Guggenheim earn DGA noms (AP)
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Original cast of 'God of Carnage' are reuniting (AP)
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SCREAM! Mary Murphy Heads Back To 'So You Think You Can Dance'! (omg!)
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Kevin James, Wife Expecting Baby No. 3 (omg!)
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Lady Gaga? Britney Spears? Who Is (Or Isn't) Performing At The Grammy Awards? (omg!)
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ROLL CALL: Kelly Clarkson Names Her Pet Goat Billy Joel (omg!)
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Big Bang Theory Renewed for Three More Years (omg!)
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National Board of Review attracts Oscar hopefuls (omg!)
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David Nelson of "Ozzie and Harriet" TV family dies (omg!)
Sports News
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Michigan gets its man, hiring Brady Hoke (AP)
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Fox finally makes it to Denver for interview (AP)
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Softball stars not playing for US team (AP)
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Qatar restore pride with China victory (AFP)
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Les Miles has a new 7-year contract at LSU (AP)
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Hoffman retires after 601 saves in 18 seasons (AP)
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Lakers crush Cavs 112-57 in best defensive effort (AP)
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Panthers hire Chargers' Rivera as head coach (AP)
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Koyie Hill, Cubs agree to $850,000 contract (AP)
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Cavaliers humiliated by 55-point loss to Lakers (Reuters)
Technology News
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Review: Technology helps golfers fine-tune game (AP)
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Verizon to start selling iPhone on Feb. 10 (AP)
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Verizon big winner from having iPhone? Not so fast (AP)
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CES 2011: End-of-show scrapbook (Ben Patterson)
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Verizon iPhone announcement gets ‘Daily Show’ treatment (Ben Patterson)
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CES Tablets Jockey for Traction Against Apple's iPad (NewsFactor)
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Do Americans Love Their Electronics? Nielsen Survey Gives Us a Glimpse (PC World)
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Treadmill Allows You to Take a Virtual Run Anywhere on Google Earth [VIDEO] (Mashable)
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Ex-RIM employee says the PlayBook faces challenges (Digital Trends)
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IBM, Samsung to jointly develop chip technology (Reuters)
Setting Up the HTML
The tabs in the tabview widget will be represented by a list of
<a>
elements whose href
attribute is set to
the id of an <div>
element that contains its content.
Therefore, without JavaScript and CSS, the tabs function as in-page links.
<h3 id="tabview-heading">Today's News</h3> <div id="tabview-1" class="yui3-tabview-loading"> <ul> <li class="yui3-tab yui-tab-selected"><a href="#top-stories"><em>Top Stories</em></a></li> <li class="yui3-tab"><a href="#world-news"><em>World</em></a></li> <li class="yui3-tab"><a href="#entertainment-news"><em>Entertainment</em></a></li> <li class="yui3-tab"><a href="#sports-news"><em>Sports</em></a></li> <li class="yui3-tab"><a href="#technology-news"><em>Technology</em></a></li> </ul> <div> <div class="yui3-tabpanel yui-tabpanel-selected" id="top-stories"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="world-news"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="entertainment-news"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="sports-news"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="technology-news"> <!-- Tab Panel Content Here --> </div> </div> </div>
<h3 id="tabview-heading">Today's News</h3> <div id="tabview-1" class="yui3-tabview-loading"> <ul> <li class="yui3-tab yui-tab-selected"><a href="#top-stories"><em>Top Stories</em></a></li> <li class="yui3-tab"><a href="#world-news"><em>World</em></a></li> <li class="yui3-tab"><a href="#entertainment-news"><em>Entertainment</em></a></li> <li class="yui3-tab"><a href="#sports-news"><em>Sports</em></a></li> <li class="yui3-tab"><a href="#technology-news"><em>Technology</em></a></li> </ul> <div> <div class="yui3-tabpanel yui-tabpanel-selected" id="top-stories"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="world-news"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="entertainment-news"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="sports-news"> <!-- Tab Panel Content Here --> </div> <div class="yui3-tabpanel" id="technology-news"> <!-- Tab Panel Content Here --> </div> </div> </div>
For this example the content of each tab panel is created on the server using the YQL API to fetch the title and URL for news stories made available from the various Yahoo! News RSS feeds. Here's the PHP:
function getFeed($sFeed) { $params = array( "q" => ('select title,link from rss where url="http://rss.news.yahoo.com/rss/$sFeed"'), "format" => "json" ); $encoded_params = array(); foreach ($params as $k => $v) { $encoded_params[] = urlencode($k)."=".urlencode($v); } $url = "http://query.yahooapis.com/v1/public/yql?".implode("&", $encoded_params); $ch = curl_init(); curl_setopt($ch, CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); $rsp = curl_exec($ch); curl_close($ch); if ($rsp !== false) { $rsp_obj = json_decode($rsp, true); $results = $rsp_obj["query"]["results"]["item"]; $list = ""; // HTML output $nResults = count($results); if ($nResults > 10) { $nResults = 9; } for ($i = 0; $i<= $nResults; $i++) { $result = $results[$i]; $list.= <<< END_OF_HTML <li> <a href="${result["link"]}"><q>${result["title"]}</q></a> </li> END_OF_HTML; } return ("<ul>" . $list . "</ul>"); } }
function getFeed($sFeed) { $params = array( "q" => ('select title,link from rss where url="http://rss.news.yahoo.com/rss/$sFeed"'), "format" => "json" ); $encoded_params = array(); foreach ($params as $k => $v) { $encoded_params[] = urlencode($k)."=".urlencode($v); } $url = "http://query.yahooapis.com/v1/public/yql?".implode("&", $encoded_params); $ch = curl_init(); curl_setopt($ch, CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); $rsp = curl_exec($ch); curl_close($ch); if ($rsp !== false) { $rsp_obj = json_decode($rsp, true); $results = $rsp_obj["query"]["results"]["item"]; $list = ""; // HTML output $nResults = count($results); if ($nResults > 10) { $nResults = 9; } for ($i = 0; $i<= $nResults; $i++) { $result = $results[$i]; $list.= <<< END_OF_HTML <li> <a href="${result["link"]}"><q>${result["title"]}</q></a> </li> END_OF_HTML; } return ("<ul>" . $list . "</ul>"); } }
Progressive Enhancement
To account for the scenario where the user has CSS enabled in their browser but JavaScript is disabled, the CSS used to style the tabview will be loaded via JavaScript using the YUI instance's built-in Loader.
YUI({ base: "../../build/", modules: { "tabviewcss": { type: "css", fullpath: "assets/tabview.css" }, "tabviewjs": { type: "js", fullpath: "assets/tabview.js", requires: ["node-focusmanager", "tabviewcss"] } }, timeout: 10000 }).use("tabviewjs");
YUI({ base: "../../build/", modules: { "tabviewcss": { type: "css", fullpath: "assets/tabview.css" }, "tabviewjs": { type: "js", fullpath: "assets/tabview.js", requires: ["node-focusmanager", "tabviewcss"] } }, timeout: 10000 }).use("tabviewjs");
To prevent the user from seeing a flash unstyled content when JavaScript is enabled,
a style rule is created using YUI's yui3-js-enabled
class name that will temporarily
hide the markup while the JavaScript and CSS are in the process of loading. For more on using the
yui3-js-enabled
class name, see the
HIDING PROGRESSIVELY ENHANCED MARKUP section of the
YUI Widget landing page.
/* Hide the list while it is being transformed into a tabview. */ .yui3-js-enabled .yui3-tabview-loading { display: none; }
/* Hide the list while it is being transformed into a tabview. */ .yui3-js-enabled .yui3-tabview-loading { display: none; }
ARIA Support
Through the use of CSS and JavaScript the HTML for the tabview can be transformed into something that looks and behaves like a desktop tab control, but users of screen readers won't perceive it as an atomic widget, but rather simply as a set of HTML elements. However, through the application of the WAI-ARIA Roles and States, it is possible to improve the semantics of the markup such that users of screen readers perceive it as a tab control.
Keyboard Functionality
The keyboard functionality for the tabview widget will be provided by the
Focus Manager Node Plugin. The Focus Manager's
descendants
attribute is set to a value of ".yui3-tab>a", so that only one tab in the tabview
is in the browser's default tab flow. This allows users navigating via the
keyboard to use the tab key to quickly move into and out of the tabview. Once
the tabview has focus, the user can move focus among each tab using the left
and right arrows keys, as defined by the value of the
keys
attribute. Lastly, the
focusClass
attribute is used to apply a class of yui-tab-focus
to the parent
<li>
of each <a>
when it is focused,
making it easy to style the tab's focused state in each of the
A-Grade browsers.
YUI().use("*", function (Y) { var tabView = Y.one("#tabview-1"), tabList = tabView.one("ul"), tabHeading = Y.one("#tabview-heading"), sInstructionalText = tabHeading.get("innerHTML"); selectedTabAnchor = tabView.one(".yui3-tab-selected>a"), bGeckoIEWin = ((Y.UA.gecko || Y.UA.ie) && navigator.userAgent.indexOf("Windows") > -1), panelMap = {}; tabView.addClass("yui3-tabview"); // Remove the "yui3-loading" class now that the necessary YUI dependencies are loaded and the // tabview has been skinned. tabView.removeClass("yui3-tabview-loading"); // Apply the ARIA roles, states and properties. // Add some instructional text to the heading that will be read by // the screen reader when the first tab in the tabview is focused. tabHeading.set("innerHTML", (sInstructionalText + " <em>Press the enter key to load the content of each tab.</em>")); tabList.setAttrs({ "aria-labelledby": "tabview-heading", role: "tablist" }); tabView.one("div").set("role", "presentation"); tabView.plug(Y.Plugin.NodeFocusManager, { descendants: ".yui3-tab>a", keys: { next: "down:39", // Right arrow previous: "down:37" }, // Left arrow focusClass: { className: "yui3-tab-focus", fn: function (node) { return node.get("parentNode"); } }, circular: true }); // If the list of tabs loses focus, set the activeDescendant // attribute to the currently selected tab. tabView.focusManager.after("focusedChange", function (event) { if (!event.newVal) { // The list of tabs has lost focus this.set("activeDescendant", selectedTabAnchor); } }); tabView.all(".yui3-tab>a").each(function (anchor) { var sHref = anchor.getAttribute("href", 2), sPanelID = sHref.substring(1, sHref.length), panel; // Apply the ARIA roles, states and properties to each tab anchor.set("role", "tab"); anchor.get("parentNode").set("role", "presentation"); // Remove the "href" attribute from the anchor element to // prevent JAWS and NVDA from reading the value of the "href" // attribute when the anchor is focused if (bGeckoIEWin) { anchor.removeAttribute("href"); } // Cache a reference to id of the tab's corresponding panel // element so that it can be made visible when the tab // is clicked. panelMap[anchor.get("id")] = sPanelID; // Apply the ARIA roles, states and properties to each panel panel = Y.one(("#" + sPanelID)); panel.setAttrs({ role: "tabpanel", "aria-labelledby": anchor.get("id") }); }); // Use the "delegate" custom event to listen for the "click" event // of each tab's <A> element. tabView.delegate("click", function (event) { var selectedPanel, sID = this.get("id"); // Deselect the currently selected tab and hide its // corresponding panel. if (selectedTabAnchor) { selectedTabAnchor.get("parentNode").removeClass("yui3-tab-selected"); Y.one(("#" + panelMap[selectedTabAnchor.get("id")])).removeClass("yui3-tabpanel-selected"); } selectedTabAnchor = this; selectedTabAnchor.get("parentNode").addClass("yui3-tab-selected"); selectedPanel = Y.one(("#" + panelMap[sID])); selectedPanel.addClass("yui3-tabpanel-selected"); creatingPaging(selectedPanel); // Prevent the browser from following the URL specified by the // anchor's "href" attribute when clicked. event.preventDefault(); }, ".yui3-tab>a"); // Since the anchor's "href" attribute has been removed, the // element will not fire the click event in Firefox when the // user presses the enter key. To fix this, dispatch the // "click" event to the anchor when the user presses the // enter key. if (bGeckoIEWin) { tabView.delegate("keydown", function (event) { if (event.charCode === 13) { this.simulate("click"); } }, ">ul>li>a"); } });
YUI().use("*", function (Y) { var tabView = Y.one("#tabview-1"), tabList = tabView.one("ul"), tabHeading = Y.one("#tabview-heading"), sInstructionalText = tabHeading.get("innerHTML"); selectedTabAnchor = tabView.one(".yui3-tab-selected>a"), bGeckoIEWin = ((Y.UA.gecko || Y.UA.ie) && navigator.userAgent.indexOf("Windows") > -1), panelMap = {}; tabView.addClass("yui3-tabview"); // Remove the "yui3-loading" class now that the necessary YUI dependencies are loaded and the // tabview has been skinned. tabView.removeClass("yui3-tabview-loading"); // Apply the ARIA roles, states and properties. // Add some instructional text to the heading that will be read by // the screen reader when the first tab in the tabview is focused. tabHeading.set("innerHTML", (sInstructionalText + " <em>Press the enter key to load the content of each tab.</em>")); tabList.setAttrs({ "aria-labelledby": "tabview-heading", role: "tablist" }); tabView.one("div").set("role", "presentation"); tabView.plug(Y.Plugin.NodeFocusManager, { descendants: ".yui3-tab>a", keys: { next: "down:39", // Right arrow previous: "down:37" }, // Left arrow focusClass: { className: "yui3-tab-focus", fn: function (node) { return node.get("parentNode"); } }, circular: true }); // If the list of tabs loses focus, set the activeDescendant // attribute to the currently selected tab. tabView.focusManager.after("focusedChange", function (event) { if (!event.newVal) { // The list of tabs has lost focus this.set("activeDescendant", selectedTabAnchor); } }); tabView.all(".yui3-tab>a").each(function (anchor) { var sHref = anchor.getAttribute("href", 2), sPanelID = sHref.substring(1, sHref.length), panel; // Apply the ARIA roles, states and properties to each tab anchor.set("role", "tab"); anchor.get("parentNode").set("role", "presentation"); // Remove the "href" attribute from the anchor element to // prevent JAWS and NVDA from reading the value of the "href" // attribute when the anchor is focused if (bGeckoIEWin) { anchor.removeAttribute("href"); } // Cache a reference to id of the tab's corresponding panel // element so that it can be made visible when the tab // is clicked. panelMap[anchor.get("id")] = sPanelID; // Apply the ARIA roles, states and properties to each panel panel = Y.one(("#" + sPanelID)); panel.setAttrs({ role: "tabpanel", "aria-labelledby": anchor.get("id") }); }); // Use the "delegate" custom event to listen for the "click" event // of each tab's <A> element. tabView.delegate("click", function (event) { var selectedPanel, sID = this.get("id"); // Deselect the currently selected tab and hide its // corresponding panel. if (selectedTabAnchor) { selectedTabAnchor.get("parentNode").removeClass("yui3-tab-selected"); Y.one(("#" + panelMap[selectedTabAnchor.get("id")])).removeClass("yui3-tabpanel-selected"); } selectedTabAnchor = this; selectedTabAnchor.get("parentNode").addClass("yui3-tab-selected"); selectedPanel = Y.one(("#" + panelMap[sID])); selectedPanel.addClass("yui3-tabpanel-selected"); creatingPaging(selectedPanel); // Prevent the browser from following the URL specified by the // anchor's "href" attribute when clicked. event.preventDefault(); }, ".yui3-tab>a"); // Since the anchor's "href" attribute has been removed, the // element will not fire the click event in Firefox when the // user presses the enter key. To fix this, dispatch the // "click" event to the anchor when the user presses the // enter key. if (bGeckoIEWin) { tabView.delegate("keydown", function (event) { if (event.charCode === 13) { this.simulate("click"); } }, ">ul>li>a"); } });
Accessibility Sugar
One of the challenges faced by users of screen readers is knowing when you've left the context of a given control. In the case of this tabview, if it were adjacent to another ARIA-enabled widget, the user would know they've left the tabview when the screen reader announces the role of the adjacent widget. However, if the tabview is sitting alongside standard HTML content, it would be really difficult for the user to know when they've left the context of the active panel.
One solution to this problem is to add some additional navigation as the last child of each tab panel that allows the user to move to the previous and next panel in the tabview. This will not only help alert users of screen readers that they've reached the end of the tab's panel, but allow all keyboard users to move more quickly to the next/previous panel. Without this additionally navigation, keyboard users would typically have to press shift+tab to navigate back up to the list of tabs to move to the next/previous tab.
var creatingPaging = function (panel) { var listitem, sHTML = ""; if (!panel.one(".paging")) { listitem = selectedTabAnchor.get("parentNode"); if (listitem.previous()) { sHTML += '<button type="button" class="yui3-tabview-prevbtn">Previous Tab Panel</button>'; } if (listitem.next()) { sHTML += '<button type="button" class="yui3-tabview-nextbtn">Next Tab Panel</button>'; } panel.append('<div class="paging">' + sHTML + '</div>'); } }; creatingPaging(Y.one(".yui3-tabpanel-selected")); tabView.delegate("click", function (event) { var node = selectedTabAnchor.get("parentNode").previous().one("a"); tabView.focusManager.focus(node); node.simulate("click"); }, ".yui3-tabview-prevbtn"); tabView.delegate("click", function (event) { var node = selectedTabAnchor.get("parentNode").next().one("a"); tabView.focusManager.focus(node); node.simulate("click"); }, ".yui3-tabview-nextbtn");
var creatingPaging = function (panel) { var listitem, sHTML = ""; if (!panel.one(".paging")) { listitem = selectedTabAnchor.get("parentNode"); if (listitem.previous()) { sHTML += '<button type="button" class="yui3-tabview-prevbtn">Previous Tab Panel</button>'; } if (listitem.next()) { sHTML += '<button type="button" class="yui3-tabview-nextbtn">Next Tab Panel</button>'; } panel.append('<div class="paging">' + sHTML + '</div>'); } }; creatingPaging(Y.one(".yui3-tabpanel-selected")); tabView.delegate("click", function (event) { var node = selectedTabAnchor.get("parentNode").previous().one("a"); tabView.focusManager.focus(node); node.simulate("click"); }, ".yui3-tabview-prevbtn"); tabView.delegate("click", function (event) { var node = selectedTabAnchor.get("parentNode").next().one("a"); tabView.focusManager.focus(node); node.simulate("click"); }, ".yui3-tabview-nextbtn");