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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Obama clears way for oil drilling off US coasts (AP)
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New England flooding drowns homes and dreams (AP)
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Chechen rebels say responsible for Moscow bombings (AP)
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European bishops urge victims to go to the police (AP)
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Barbara Bush released from Houston hospital (AP)
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US Navy plane crashes in Arabian Sea (AP)
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Factory orders rise for 10th time in 11 months (AP)
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Study suggests toads can detect coming earthquakes (AP)
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Palin's show drops LL Cool J after he complains (AP)
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Twins' Span hits mom with foul ball, but she's OK (AP)
World News
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Chechen rebels say responsible for Moscow bombings (AP)
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Pakistani lawmakers target presidential powers (AP)
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Maneuvering in Iraq intensifies over who to lead (AP)
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Swiss to decide on Polanski after Calif. ruling (AP)
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European bishops urge victims to go to the police (AP)
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Why the Moscow Bombings Weren't Breaking News in Russia (Time.com)
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Italian politicians rally to pope's defense (AP)
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Sudan opposition mulls boycotting elections (AP)
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Last stand for opposition in Bolivia elections (AP)
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Zimbabwe's Mugabe names rights, election groups (Reuters)
Entertainment News
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Veteran 'Wire,' 'ER' screenwriter David Mills dies (AP)
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Swiss to decide on Polanski after Calif. ruling (AP)
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Lindsey Vonn gets her `Law & Order' wish next week (AP)
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Palin's show drops LL Cool J after he complains (AP)
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`Modern Family,' `Glee' among Peabody winners (AP)
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Jesse James reportedly seeking professional help (AP)
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Veteran 'Wire,' 'ER' screenwriter David Mills dies (AP)
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Swiss to decide on Polanski after Calif. ruling (AP)
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Review: Hall & Oates covers have little buzz (AP)
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EMI needs fresh cash as licensing talks collapse (Reuters)
Sports News
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UConn, Griner headline intriguing Final Four field (AP)
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Twins' Span hits mom with foul ball, but she's OK (AP)
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Berkman goes on DL with nagging knee injury (AP)
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Vick legacy: Dogfighting probes spike in Philadelphia (AP)
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Hamlin has surgery on left knee (AP)
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Tar Heels, Flyers to play for NIT title (AP)
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Vikings sign defensive end Mike Montgomery from Packers (Reuters)
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MLB exploring spring training in Italy (AP)
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Nash helps Suns clinch playoff spot (AP)
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Freshman Dawkins: Duke's X-factor? (AP)
Technology News
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Google: Online attacks aimed at Vietnam's critics (AP)
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Google service disruption bodes ill for Chinese (AP)
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Journalists in China say Yahoo accounts hacked (AP)
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At Facebook, 'Fans' are out, 'Like' is in (Christopher Null)
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AT&T racing to shore up wireless network, Journal reports (Ben Patterson)
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Gov't set to ban texting by truck, bus drivers (AP)
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Google has censorship balancing act outside China (AP)
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MobileMe Gallery app updated, adds contacts feature (Macworld.com)
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Meru Networks shares soar in IPO debut (AP)
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Microsoft to Release 64GB Zune HD April 12 (PC Magazine)
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"> <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"> <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
The markup above will be transformed using both CSS and JavaScript. 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.
Additionally, a small block of JavaScript will be placed in the
<head>
used to temporarily hide the markup
while the JavaScript and CSS are in the process of loading to prevent the user
from seeing a flash unstyled content.
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", function(Y, result) { // The callback supplied to use() will be executed regardless of // whether the operation was successful or not. The second parameter // is a result object that has the status of the operation. We can // use this to try to recover from failures or timeouts. if (!result.success) { Y.log("Load failure: " + result.msg, "warn", "Example"); // Show the tabview HTML if the loader failed that way the // original unskinned tabview will be visible so that the // user can interact with it either way. document.documentElement.className = ""; } });
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", function(Y, result) { // The callback supplied to use() will be executed regardless of // whether the operation was successful or not. The second parameter // is a result object that has the status of the operation. We can // use this to try to recover from failures or timeouts. if (!result.success) { Y.log("Load failure: " + result.msg, "warn", "Example"); // Show the tabview HTML if the loader failed that way the // original unskinned tabview will be visible so that the // user can interact with it either way. document.documentElement.className = ""; } });
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("yui-tabview"); // Remove the "yui-loading" class from the documentElement // now that the necessary YUI dependencies are loaded and the // tabview has been skinned. tabView.get("ownerDocument").get("documentElement").removeClass("yui-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: "yui-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("yui-tab-selected"); Y.one(("#" + panelMap[selectedTabAnchor.get("id")])).removeClass("yui-tabpanel-selected"); } selectedTabAnchor = this; selectedTabAnchor.get("parentNode").addClass("yui-tab-selected"); selectedPanel = Y.one(("#" + panelMap[sID])); selectedPanel.addClass("yui-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("yui-tabview"); // Remove the "yui-loading" class from the documentElement // now that the necessary YUI dependencies are loaded and the // tabview has been skinned. tabView.get("ownerDocument").get("documentElement").removeClass("yui-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: "yui-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("yui-tab-selected"); Y.one(("#" + panelMap[selectedTabAnchor.get("id")])).removeClass("yui-tabpanel-selected"); } selectedTabAnchor = this; selectedTabAnchor.get("parentNode").addClass("yui-tab-selected"); selectedPanel = Y.one(("#" + panelMap[sID])); selectedPanel.addClass("yui-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, paging; if (!panel.one(".paging")) { listitem = selectedTabAnchor.get("parentNode"); sHTML = ""; 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>'; } paging = Y.Node.create('<div class="paging">' + sHTML + '</div>'); panel.appendChild(paging); } }; 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, paging; if (!panel.one(".paging")) { listitem = selectedTabAnchor.get("parentNode"); sHTML = ""; 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>'; } paging = Y.Node.create('<div class="paging">' + sHTML + '</div>'); panel.appendChild(paging); } }; 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");