diff --git a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js
index 585eae029ab..eb43274978e 100644
--- a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js
+++ b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js
@@ -125,6 +125,9 @@ Y.extend(DIALOGUE, Y.Panel, {
         }
 
         if (this.get('modal')) {
+            // If we're a modal then make sure our container is ARIA
+            // hidden by default. ARIA visibility is managed for modal dialogues.
+            this.get(BASE).set('aria-hidden', 'true');
             this.plug(Y.M.core.LockScroll);
         }
 
@@ -363,6 +366,13 @@ Y.extend(DIALOGUE, Y.Panel, {
             this.lockScroll.enableScrollLock(this.shouldResizeFullscreen());
         }
 
+        // Only do accessibility hiding for modals because the ARIA spec
+        // says that all ARIA dialogues should be modal.
+        if (this.get('modal')) {
+            // Make this dialogue visible to screen readers.
+            this.setAccessibilityVisible();
+        }
+
         // Try and find a node to focus on using the focusOnShowSelector attribute.
         if (focusSelector !== null) {
             focusNode = this.get('boundingBox').one(focusSelector);
@@ -390,6 +400,11 @@ Y.extend(DIALOGUE, Y.Panel, {
             }
         }
 
+        if (this.get('modal')) {
+            // Hide this dialogue from screen readers.
+            this.setAccessibilityHidden();
+        }
+
         // Unlock scroll if the plugin is present.
         if (this.lockScroll) {
             this.lockScroll.disableScrollLock();
@@ -434,6 +449,73 @@ Y.extend(DIALOGUE, Y.Panel, {
         } else if (target === firstitem && direction === 'backward') {  // Tab+shift key.
             return lastitem.focus();
         }
+    },
+
+    /**
+     * Sets the appropriate aria attributes on this dialogue and the other
+     * elements in the DOM to ensure that screen readers are able to navigate
+     * the dialogue popup correctly.
+     *
+     * @method setAccessibilityVisible
+     */
+    setAccessibilityVisible: function() {
+        // Get the element that contains this dialogue because we need it
+        // to filter out from the document.body child elements.
+        var container = this.get(BASE);
+        // Keep a record of any elements we change so that they can be reverted later.
+        this.hiddenSiblings = [];
+
+        // We need to get a list containing each sibling element and the shallowest
+        // non-ancestral nodes in the DOM. We can shortcut this a little by leveraging
+        // the fact that this dialogue is always appended to the document body therefore
+        // it's siblings are the shallowest non-ancestral nodes. If that changes then
+        // this code should also be updated.
+        Y.one(document.body).get('children').each(function(node) {
+            // Skip the element that contains us.
+            if (node !== container) {
+                var hidden = node.get('aria-hidden');
+                // If they are already hidden we can ignore them.
+                if (hidden !== 'true') {
+                    // Save their current state.
+                    node.setData('previous-aria-hidden', hidden);
+                    this.hiddenSiblings.push(node);
+
+                    // Hide this node from screen readers.
+                    node.set('aria-hidden', 'true');
+                }
+            }
+        }, this);
+
+        // Make us visible to screen readers.
+        container.set('aria-hidden', 'false');
+    },
+
+    /**
+     * Restores the aria visibility on the DOM elements changed when displaying
+     * the dialogue popup and makes the dialogue aria hidden to allow screen
+     * readers to navigate the main page correctly when the dialogue is closed.
+     *
+     * @method setAccessibilityHidden
+     */
+    setAccessibilityHidden: function() {
+        var container = this.get(BASE);
+        container.set('aria-hidden', 'true');
+
+        // Restore the sibling nodes back to their original values.
+        Y.Array.each(this.hiddenSiblings, function(node) {
+            var previousValue = node.getData('previous-aria-hidden');
+            // If the element didn't previously have an aria-hidden attribute
+            // then we can just remove the one we set.
+            if (previousValue === null) {
+                node.removeAttribute('aria-hidden');
+            } else {
+                // Otherwise set it back to the old value (which will be false).
+                node.set('aria-hidden', previousValue);
+            }
+        });
+
+        // Clear the cache. No longer need to store these.
+        this.hiddenSiblings = [];
     }
 }, {
     NAME : DIALOGUE_NAME,
diff --git a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js
index 70121903bb1..5d740f86e12 100644
--- a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js
+++ b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js
@@ -1,2 +1,2 @@
-YUI.add("moodle-core-notification-dialogue",function(e,t){var n,r,i,s,o,u,a;n="moodle-dialogue",r="notificationBase",i="yesLabel",s="noLabel",o="title",u="question",a={BASE:"moodle-dialogue-base",WRAP:"moodle-dialogue-wrap",HEADER:"moodle-dialogue-hd",BODY:"moodle-dialogue-bd",CONTENT:"moodle-dialogue-content",FOOTER:"moodle-dialogue-ft",HIDDEN:"hidden",LIGHTBOX:"moodle-dialogue-lightbox"},M.core=M.core||{};var f="Moodle dialogue",l,c=n+"-fullscreen",h=n+"-hidden",p=" [role=dialog]",d="[role=menubar]",v=".",m="moodle-has-zindex",g='input:not([type="hidden"]), a[href], button, textarea, select, [tabindex]';l=function(t){var n=e.clone(t);n.COUNT=e.stamp(this);var r="moodle-dialogue-"+n.COUNT;n.notificationBase=e.Node.create('<div class="'+a.BASE+'">').append(e.Node.create('<div id="'+r+'" role="dialog" aria-labelledby="'+r+'-header-text" class="'+a.WRAP+'"></div>').append(e.Node.create('<div id="'+r+'-header-text" class="'+a.HEADER+' yui3-widget-hd"></div>')).append(e.Node.create('<div class="'+a.BODY+' yui3-widget-bd"></div>')).append(e.Node.create('<div class="'+a.FOOTER+' yui3-widget-ft"></div>'))),e.one(document.body).append(n.notificationBase),n.additionalBaseClass&&n.notificationBase.addClass(n.additionalBaseClass),n.srcNode="#"+r,n.closeButton===!1?n.buttons=null:n.buttons=[{section:e.WidgetStdMod.HEADER,classNames:"closebutton",action:function(){this.hide()}}],l.superclass.constructor.apply(this,[n]),n.closeButton!==!1&&this.get("buttons").header[0].setAttribute("title",this.get("closeButtonTitle"))},e.extend(l,e.Panel,{_resizeevent:null,_orientationevent:null,_calculatedzindex:!1,_originalPosition:null,initializer:function(){var t;this.get("render")&&this.render(),this.after("visibleChange",this.visibilityChanged,this),this.get("center")&&this.centerDialogue(),this.get("modal")&&this.plug(e.M.core.LockScroll),t=this.get("boundingBox"),t.addClass(m),e.Array.each(this.get("extraClasses"),t.addClass,t),this.get("visible")&&this.applyZIndex(),this.on("maskShow",this.applyZIndex),this.on("maskShow",function(){var t=e.one(e.config.win),n=this.get("boundingBox");this.get("center")||(this._originalPosition=n.getXY()),n.getStyle("position")!=="fixed"&&n.setStyles({top:t.get("scrollTop"),left:t.get("scrollLeft")})},this),this.after("destroyedChange",function(){this.get(r).remove(!0)},this)},applyZIndex:function(){var t=1,n=1,r=this.get("boundingBox"),i=this.get("maskNode"),s=this.get("zIndex");s!==0&&!this._calculatedzindex?r.setStyle("zIndex",s):(e.all(p+", "+d+", "+v+m).each(function(e){var n=this.findZIndex(e);n>t&&(t=n)},this),n=(t+1).toString(),r.setStyle("zIndex",n),this.set("zIndex",n),this.get("modal")&&(i.setStyle("zIndex",n),e.UA.ie&&e.UA.compareVersions(e.UA.ie,9)<0&&setTimeout(function(){i.setStyle("position","static"),setTimeout(function(){i.setStyle("position","fixed")},0)},0)),this._calculatedzindex=!0)},findZIndex:function(e){var t=e.getStyle("zIndex")||e.ancestor().getStyle("zIndex");return t?parseInt(t,10):0},visibilityChanged:function(t){var n,r;t.attrName==="visible"&&(this.get("maskNode").addClass(a.LIGHTBOX),t.prevVal&&!t.newVal&&(r=this.get("boundingBox"),this._resizeevent&&(this._resizeevent.detach(),this._resizeevent=null),this._orientationevent&&(this._orientationevent.detach(),this._orientationevent=null),r.detach("key",this.keyDelegation)),!t.prevVal&&t.newVal&&(this.applyZIndex(),this.makeResponsive(),this.shouldResizeFullscreen()||this.get("draggable")&&(n="#"+this.get("id")+" ."+a.HEADER,this.plug(e.Plugin.Drag,{handles:[n]}),e.one(n).setStyle("cursor","move")),this.keyDelegation()),this.get("center")&&!t.prevVal&&t.newVal&&this.centerDialogue())},makeResponsive:function(){var e=this.get("boundingBox");this.shouldResizeFullscreen()?(e.addClass(c),e.setStyles({left:null,top:null,width:null,height:null,right:null,bottom:null})):this.get("responsive")&&e.removeClass(c).setStyles({width:this.get("width"),height:this.get("height")})},centerDialogue:function(){var t=this.get("boundingBox"),n=t.hasClass(h),r,i;if(this.shouldResizeFullscreen())return;n&&t.setStyle("top","-1000px").removeClass(h),r=Math.max(Math.round((t.get("winWidth")-t.get("offsetWidth"))/2),15),i=Math.max(Math.round((t.get("winHeight")-t.get("offsetHeight"))/2),15)+e.one(window).get("scrollTop"),t.setStyles({left:r,top:i}),n&&t.addClass(h),this.makeResponsive()},shouldResizeFullscreen:function(){return window===window.parent&&this.get("responsive")&&Math.floor(e.one(document.body).get("winWidth"))<this.get("responsiveWidth")},show:function(){var e=null,t=this.headerNode,n=this.bodyNode,r=this.get("focusOnShowSelector"),i=null;return e=l.superclass.show.call(this),!this.get("center")&&this._originalPosition&&this.get("boundingBox").setXY(this._originalPosition),this.lockScroll&&this.lockScroll.enableScrollLock(this.shouldResizeFullscreen()),r!==null&&(i=this.get("boundingBox").one(r)),i||(t&&t!==""?i=t:n&&n!==""&&(i=n)),i&&i.focus(),e},hide:function(e){if(e&&e.type==="key"&&e.keyCode===27&&!this.get("focused"))return;return this.lockScroll&&this.lockScroll.disableScrollLock(),l.superclass.hide.call(this,arguments)},keyDelegation:function(){var e=this.get("boundingBox");e.delegate("key",function(e){var t=e.target,n="forward";e.shiftKey&&(n="backward"),this.trapFocus(t,n)&&e.preventDefault()},"down:9",g,this)},trapFocus:function(e,t){var n=this.get("boundingBox"),r=n.one(g),i=n.all(g).pop();if(e===i&&t==="forward")return r.focus();if(e===r&&t==="backward")return i.focus()}},{NAME:f,CSS_PREFIX:n,ATTRS:{notificationBase:{},lightbox:{lazyAdd:!1,setter:function(e){this.set("modal",e)}},closeButton:{validator:e.Lang.isBoolean,value:!0},closeButtonTitle:{validator:e.Lang.isString,value:M.util.get_string("closebuttontitle","moodle")},center:{validator:e.Lang.isBoolean,value:!0},draggable:{validator:e.Lang.isBoolean,value:!1},COUNT:{value:null},responsive:{validator:e.Lang.isBoolean,value:!0},responsiveWidth:{value:768},focusOnShowSelector:{value:null}}}),e.Base.modifyAttrs(l,{width:{value:"400px",setter:function(
-e){return e==="auto"?"":e}},visible:{value:!1},centered:{setter:function(e){return e&&this.set("center",!0),!1}},render:{value:!0,writeOnce:!0},extraClasses:{value:[]}}),e.Base.mix(l,[e.M.core.WidgetFocusAfterHide]),M.core.dialogue=l;var y=function(){y.superclass.constructor.apply(this,arguments)};e.extend(y,M.core.dialogue,{initializer:function(){this.show()}},{NAME:"Moodle information dialogue",CSS_PREFIX:n}),e.Base.modifyAttrs(y,{modal:{validator:e.Lang.isBoolean,value:!0}}),M.core.notification=M.core.notification||{},M.core.notification.info=y},"@VERSION@",{requires:["base","node","panel","escape","event-key","dd-plugin","moodle-core-widget-focusafterclose","moodle-core-lockscroll"]});
+YUI.add("moodle-core-notification-dialogue",function(e,t){var n,r,i,s,o,u,a;n="moodle-dialogue",r="notificationBase",i="yesLabel",s="noLabel",o="title",u="question",a={BASE:"moodle-dialogue-base",WRAP:"moodle-dialogue-wrap",HEADER:"moodle-dialogue-hd",BODY:"moodle-dialogue-bd",CONTENT:"moodle-dialogue-content",FOOTER:"moodle-dialogue-ft",HIDDEN:"hidden",LIGHTBOX:"moodle-dialogue-lightbox"},M.core=M.core||{};var f="Moodle dialogue",l,c=n+"-fullscreen",h=n+"-hidden",p=" [role=dialog]",d="[role=menubar]",v=".",m="moodle-has-zindex",g='input:not([type="hidden"]), a[href], button, textarea, select, [tabindex]';l=function(t){var n=e.clone(t);n.COUNT=e.stamp(this);var r="moodle-dialogue-"+n.COUNT;n.notificationBase=e.Node.create('<div class="'+a.BASE+'">').append(e.Node.create('<div id="'+r+'" role="dialog" aria-labelledby="'+r+'-header-text" class="'+a.WRAP+'"></div>').append(e.Node.create('<div id="'+r+'-header-text" class="'+a.HEADER+' yui3-widget-hd"></div>')).append(e.Node.create('<div class="'+a.BODY+' yui3-widget-bd"></div>')).append(e.Node.create('<div class="'+a.FOOTER+' yui3-widget-ft"></div>'))),e.one(document.body).append(n.notificationBase),n.additionalBaseClass&&n.notificationBase.addClass(n.additionalBaseClass),n.srcNode="#"+r,n.closeButton===!1?n.buttons=null:n.buttons=[{section:e.WidgetStdMod.HEADER,classNames:"closebutton",action:function(){this.hide()}}],l.superclass.constructor.apply(this,[n]),n.closeButton!==!1&&this.get("buttons").header[0].setAttribute("title",this.get("closeButtonTitle"))},e.extend(l,e.Panel,{_resizeevent:null,_orientationevent:null,_calculatedzindex:!1,_originalPosition:null,initializer:function(){var t;this.get("render")&&this.render(),this.after("visibleChange",this.visibilityChanged,this),this.get("center")&&this.centerDialogue(),this.get("modal")&&(this.get(r).set("aria-hidden","true"),this.plug(e.M.core.LockScroll)),t=this.get("boundingBox"),t.addClass(m),e.Array.each(this.get("extraClasses"),t.addClass,t),this.get("visible")&&this.applyZIndex(),this.on("maskShow",this.applyZIndex),this.on("maskShow",function(){var t=e.one(e.config.win),n=this.get("boundingBox");this.get("center")||(this._originalPosition=n.getXY()),n.getStyle("position")!=="fixed"&&n.setStyles({top:t.get("scrollTop"),left:t.get("scrollLeft")})},this),this.after("destroyedChange",function(){this.get(r).remove(!0)},this)},applyZIndex:function(){var t=1,n=1,r=this.get("boundingBox"),i=this.get("maskNode"),s=this.get("zIndex");s!==0&&!this._calculatedzindex?r.setStyle("zIndex",s):(e.all(p+", "+d+", "+v+m).each(function(e){var n=this.findZIndex(e);n>t&&(t=n)},this),n=(t+1).toString(),r.setStyle("zIndex",n),this.set("zIndex",n),this.get("modal")&&(i.setStyle("zIndex",n),e.UA.ie&&e.UA.compareVersions(e.UA.ie,9)<0&&setTimeout(function(){i.setStyle("position","static"),setTimeout(function(){i.setStyle("position","fixed")},0)},0)),this._calculatedzindex=!0)},findZIndex:function(e){var t=e.getStyle("zIndex")||e.ancestor().getStyle("zIndex");return t?parseInt(t,10):0},visibilityChanged:function(t){var n,r;t.attrName==="visible"&&(this.get("maskNode").addClass(a.LIGHTBOX),t.prevVal&&!t.newVal&&(r=this.get("boundingBox"),this._resizeevent&&(this._resizeevent.detach(),this._resizeevent=null),this._orientationevent&&(this._orientationevent.detach(),this._orientationevent=null),r.detach("key",this.keyDelegation)),!t.prevVal&&t.newVal&&(this.applyZIndex(),this.makeResponsive(),this.shouldResizeFullscreen()||this.get("draggable")&&(n="#"+this.get("id")+" ."+a.HEADER,this.plug(e.Plugin.Drag,{handles:[n]}),e.one(n).setStyle("cursor","move")),this.keyDelegation()),this.get("center")&&!t.prevVal&&t.newVal&&this.centerDialogue())},makeResponsive:function(){var e=this.get("boundingBox");this.shouldResizeFullscreen()?(e.addClass(c),e.setStyles({left:null,top:null,width:null,height:null,right:null,bottom:null})):this.get("responsive")&&e.removeClass(c).setStyles({width:this.get("width"),height:this.get("height")})},centerDialogue:function(){var t=this.get("boundingBox"),n=t.hasClass(h),r,i;if(this.shouldResizeFullscreen())return;n&&t.setStyle("top","-1000px").removeClass(h),r=Math.max(Math.round((t.get("winWidth")-t.get("offsetWidth"))/2),15),i=Math.max(Math.round((t.get("winHeight")-t.get("offsetHeight"))/2),15)+e.one(window).get("scrollTop"),t.setStyles({left:r,top:i}),n&&t.addClass(h),this.makeResponsive()},shouldResizeFullscreen:function(){return window===window.parent&&this.get("responsive")&&Math.floor(e.one(document.body).get("winWidth"))<this.get("responsiveWidth")},show:function(){var e=null,t=this.headerNode,n=this.bodyNode,r=this.get("focusOnShowSelector"),i=null;return e=l.superclass.show.call(this),!this.get("center")&&this._originalPosition&&this.get("boundingBox").setXY(this._originalPosition),this.lockScroll&&this.lockScroll.enableScrollLock(this.shouldResizeFullscreen()),this.get("modal")&&this.setAccessibilityVisible(),r!==null&&(i=this.get("boundingBox").one(r)),i||(t&&t!==""?i=t:n&&n!==""&&(i=n)),i&&i.focus(),e},hide:function(e){if(e&&e.type==="key"&&e.keyCode===27&&!this.get("focused"))return;return this.get("modal")&&this.setAccessibilityHidden(),this.lockScroll&&this.lockScroll.disableScrollLock(),l.superclass.hide.call(this,arguments)},keyDelegation:function(){var e=this.get("boundingBox");e.delegate("key",function(e){var t=e.target,n="forward";e.shiftKey&&(n="backward"),this.trapFocus(t,n)&&e.preventDefault()},"down:9",g,this)},trapFocus:function(e,t){var n=this.get("boundingBox"),r=n.one(g),i=n.all(g).pop();if(e===i&&t==="forward")return r.focus();if(e===r&&t==="backward")return i.focus()},setAccessibilityVisible:function(){var t=this.get(r);this.hiddenSiblings=[],e.one(document.body).get("children").each(function(e){if(e!==t){var n=e.get("aria-hidden");n!=="true"&&(e.setData("previous-aria-hidden",n),this.hiddenSiblings.push(e),e.set("aria-hidden","true"))}},this),t.set("aria-hidden","false")},setAccessibilityHidden:function(){var t=this.get(r);t.set("aria-hidden","true"),e.Array.each
+(this.hiddenSiblings,function(e){var t=e.getData("previous-aria-hidden");t===null?e.removeAttribute("aria-hidden"):e.set("aria-hidden",t)}),this.hiddenSiblings=[]}},{NAME:f,CSS_PREFIX:n,ATTRS:{notificationBase:{},lightbox:{lazyAdd:!1,setter:function(e){this.set("modal",e)}},closeButton:{validator:e.Lang.isBoolean,value:!0},closeButtonTitle:{validator:e.Lang.isString,value:M.util.get_string("closebuttontitle","moodle")},center:{validator:e.Lang.isBoolean,value:!0},draggable:{validator:e.Lang.isBoolean,value:!1},COUNT:{value:null},responsive:{validator:e.Lang.isBoolean,value:!0},responsiveWidth:{value:768},focusOnShowSelector:{value:null}}}),e.Base.modifyAttrs(l,{width:{value:"400px",setter:function(e){return e==="auto"?"":e}},visible:{value:!1},centered:{setter:function(e){return e&&this.set("center",!0),!1}},render:{value:!0,writeOnce:!0},extraClasses:{value:[]}}),e.Base.mix(l,[e.M.core.WidgetFocusAfterHide]),M.core.dialogue=l;var y=function(){y.superclass.constructor.apply(this,arguments)};e.extend(y,M.core.dialogue,{initializer:function(){this.show()}},{NAME:"Moodle information dialogue",CSS_PREFIX:n}),e.Base.modifyAttrs(y,{modal:{validator:e.Lang.isBoolean,value:!0}}),M.core.notification=M.core.notification||{},M.core.notification.info=y},"@VERSION@",{requires:["base","node","panel","escape","event-key","dd-plugin","moodle-core-widget-focusafterclose","moodle-core-lockscroll"]});
diff --git a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js
index 3abe469ec19..1c57347ac2c 100644
--- a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js
+++ b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js
@@ -125,6 +125,9 @@ Y.extend(DIALOGUE, Y.Panel, {
         }
 
         if (this.get('modal')) {
+            // If we're a modal then make sure our container is ARIA
+            // hidden by default. ARIA visibility is managed for modal dialogues.
+            this.get(BASE).set('aria-hidden', 'true');
             this.plug(Y.M.core.LockScroll);
         }
 
@@ -363,6 +366,13 @@ Y.extend(DIALOGUE, Y.Panel, {
             this.lockScroll.enableScrollLock(this.shouldResizeFullscreen());
         }
 
+        // Only do accessibility hiding for modals because the ARIA spec
+        // says that all ARIA dialogues should be modal.
+        if (this.get('modal')) {
+            // Make this dialogue visible to screen readers.
+            this.setAccessibilityVisible();
+        }
+
         // Try and find a node to focus on using the focusOnShowSelector attribute.
         if (focusSelector !== null) {
             focusNode = this.get('boundingBox').one(focusSelector);
@@ -390,6 +400,11 @@ Y.extend(DIALOGUE, Y.Panel, {
             }
         }
 
+        if (this.get('modal')) {
+            // Hide this dialogue from screen readers.
+            this.setAccessibilityHidden();
+        }
+
         // Unlock scroll if the plugin is present.
         if (this.lockScroll) {
             this.lockScroll.disableScrollLock();
@@ -434,6 +449,73 @@ Y.extend(DIALOGUE, Y.Panel, {
         } else if (target === firstitem && direction === 'backward') {  // Tab+shift key.
             return lastitem.focus();
         }
+    },
+
+    /**
+     * Sets the appropriate aria attributes on this dialogue and the other
+     * elements in the DOM to ensure that screen readers are able to navigate
+     * the dialogue popup correctly.
+     *
+     * @method setAccessibilityVisible
+     */
+    setAccessibilityVisible: function() {
+        // Get the element that contains this dialogue because we need it
+        // to filter out from the document.body child elements.
+        var container = this.get(BASE);
+        // Keep a record of any elements we change so that they can be reverted later.
+        this.hiddenSiblings = [];
+
+        // We need to get a list containing each sibling element and the shallowest
+        // non-ancestral nodes in the DOM. We can shortcut this a little by leveraging
+        // the fact that this dialogue is always appended to the document body therefore
+        // it's siblings are the shallowest non-ancestral nodes. If that changes then
+        // this code should also be updated.
+        Y.one(document.body).get('children').each(function(node) {
+            // Skip the element that contains us.
+            if (node !== container) {
+                var hidden = node.get('aria-hidden');
+                // If they are already hidden we can ignore them.
+                if (hidden !== 'true') {
+                    // Save their current state.
+                    node.setData('previous-aria-hidden', hidden);
+                    this.hiddenSiblings.push(node);
+
+                    // Hide this node from screen readers.
+                    node.set('aria-hidden', 'true');
+                }
+            }
+        }, this);
+
+        // Make us visible to screen readers.
+        container.set('aria-hidden', 'false');
+    },
+
+    /**
+     * Restores the aria visibility on the DOM elements changed when displaying
+     * the dialogue popup and makes the dialogue aria hidden to allow screen
+     * readers to navigate the main page correctly when the dialogue is closed.
+     *
+     * @method setAccessibilityHidden
+     */
+    setAccessibilityHidden: function() {
+        var container = this.get(BASE);
+        container.set('aria-hidden', 'true');
+
+        // Restore the sibling nodes back to their original values.
+        Y.Array.each(this.hiddenSiblings, function(node) {
+            var previousValue = node.getData('previous-aria-hidden');
+            // If the element didn't previously have an aria-hidden attribute
+            // then we can just remove the one we set.
+            if (previousValue === null) {
+                node.removeAttribute('aria-hidden');
+            } else {
+                // Otherwise set it back to the old value (which will be false).
+                node.set('aria-hidden', previousValue);
+            }
+        });
+
+        // Clear the cache. No longer need to store these.
+        this.hiddenSiblings = [];
     }
 }, {
     NAME : DIALOGUE_NAME,
diff --git a/lib/yui/src/notification/js/dialogue.js b/lib/yui/src/notification/js/dialogue.js
index 77553ea5d72..da3fde6f427 100644
--- a/lib/yui/src/notification/js/dialogue.js
+++ b/lib/yui/src/notification/js/dialogue.js
@@ -96,6 +96,9 @@ Y.extend(DIALOGUE, Y.Panel, {
         }
 
         if (this.get('modal')) {
+            // If we're a modal then make sure our container is ARIA
+            // hidden by default. ARIA visibility is managed for modal dialogues.
+            this.get(BASE).set('aria-hidden', 'true');
             this.plug(Y.M.core.LockScroll);
         }
 
@@ -334,6 +337,13 @@ Y.extend(DIALOGUE, Y.Panel, {
             this.lockScroll.enableScrollLock(this.shouldResizeFullscreen());
         }
 
+        // Only do accessibility hiding for modals because the ARIA spec
+        // says that all ARIA dialogues should be modal.
+        if (this.get('modal')) {
+            // Make this dialogue visible to screen readers.
+            this.setAccessibilityVisible();
+        }
+
         // Try and find a node to focus on using the focusOnShowSelector attribute.
         if (focusSelector !== null) {
             focusNode = this.get('boundingBox').one(focusSelector);
@@ -361,6 +371,11 @@ Y.extend(DIALOGUE, Y.Panel, {
             }
         }
 
+        if (this.get('modal')) {
+            // Hide this dialogue from screen readers.
+            this.setAccessibilityHidden();
+        }
+
         // Unlock scroll if the plugin is present.
         if (this.lockScroll) {
             this.lockScroll.disableScrollLock();
@@ -405,6 +420,73 @@ Y.extend(DIALOGUE, Y.Panel, {
         } else if (target === firstitem && direction === 'backward') {  // Tab+shift key.
             return lastitem.focus();
         }
+    },
+
+    /**
+     * Sets the appropriate aria attributes on this dialogue and the other
+     * elements in the DOM to ensure that screen readers are able to navigate
+     * the dialogue popup correctly.
+     *
+     * @method setAccessibilityVisible
+     */
+    setAccessibilityVisible: function() {
+        // Get the element that contains this dialogue because we need it
+        // to filter out from the document.body child elements.
+        var container = this.get(BASE);
+        // Keep a record of any elements we change so that they can be reverted later.
+        this.hiddenSiblings = [];
+
+        // We need to get a list containing each sibling element and the shallowest
+        // non-ancestral nodes in the DOM. We can shortcut this a little by leveraging
+        // the fact that this dialogue is always appended to the document body therefore
+        // it's siblings are the shallowest non-ancestral nodes. If that changes then
+        // this code should also be updated.
+        Y.one(document.body).get('children').each(function(node) {
+            // Skip the element that contains us.
+            if (node !== container) {
+                var hidden = node.get('aria-hidden');
+                // If they are already hidden we can ignore them.
+                if (hidden !== 'true') {
+                    // Save their current state.
+                    node.setData('previous-aria-hidden', hidden);
+                    this.hiddenSiblings.push(node);
+
+                    // Hide this node from screen readers.
+                    node.set('aria-hidden', 'true');
+                }
+            }
+        }, this);
+
+        // Make us visible to screen readers.
+        container.set('aria-hidden', 'false');
+    },
+
+    /**
+     * Restores the aria visibility on the DOM elements changed when displaying
+     * the dialogue popup and makes the dialogue aria hidden to allow screen
+     * readers to navigate the main page correctly when the dialogue is closed.
+     *
+     * @method setAccessibilityHidden
+     */
+    setAccessibilityHidden: function() {
+        var container = this.get(BASE);
+        container.set('aria-hidden', 'true');
+
+        // Restore the sibling nodes back to their original values.
+        Y.Array.each(this.hiddenSiblings, function(node) {
+            var previousValue = node.getData('previous-aria-hidden');
+            // If the element didn't previously have an aria-hidden attribute
+            // then we can just remove the one we set.
+            if (previousValue === null) {
+                node.removeAttribute('aria-hidden');
+            } else {
+                // Otherwise set it back to the old value (which will be false).
+                node.set('aria-hidden', previousValue);
+            }
+        });
+
+        // Clear the cache. No longer need to store these.
+        this.hiddenSiblings = [];
     }
 }, {
     NAME : DIALOGUE_NAME,