HTML - implement the labels attribute

19 files changed, 296 insertions, 44 deletions

diff --git a/dom/base/FragmentOrElement.cpp b/dom/base/FragmentOrElement.cpp
index 293177ce7..3112515ff 100644
--- a/dom/base/FragmentOrElement.cpp
+++ b/dom/base/FragmentOrElement.cpp
@@ -574,6 +574,9 @@ FragmentOrElement::nsDOMSlots::Traverse(nsCycleCollectionTraversalCallback &cb,
   NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mSlots->mChildrenList");
   cb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsIDOMNodeList*, mChildrenList));
 
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mSlots->mLabelsList");
+  cb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsIDOMNodeList*, mLabelsList));
+
   NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mSlots->mClassList");
   cb.NoteXPCOMChild(mClassList.get());
 
@@ -602,6 +605,7 @@ FragmentOrElement::nsDOMSlots::Unlink(bool aIsXUL)
   mShadowRoot = nullptr;
   mContainingShadow = nullptr;
   mChildrenList = nullptr;
+  mLabelsList = nullptr;
   mCustomElementData = nullptr;
   mClassList = nullptr;
 }
diff --git a/dom/base/FragmentOrElement.h b/dom/base/FragmentOrElement.h
index 3cb5575fe..1cd8033bb 100644
--- a/dom/base/FragmentOrElement.h
+++ b/dom/base/FragmentOrElement.h
@@ -24,6 +24,7 @@
 
 class ContentUnbinder;
 class nsContentList;
+class nsLabelsNodeList;
 class nsDOMAttributeMap;
 class nsDOMTokenList;
 class nsIControllers;
@@ -313,6 +314,11 @@ public:
      */
     RefPtr<nsDOMTokenList> mClassList;
 
+    /*
+     * An object implementing the .labels property for this element.
+     */
+    RefPtr<nsLabelsNodeList> mLabelsList;
+
     /**
      * ShadowRoot bound to the element.
      */
diff --git a/dom/base/nsContentList.cpp b/dom/base/nsContentList.cpp
index 09e949009..43e65777d 100644
--- a/dom/base/nsContentList.cpp
+++ b/dom/base/nsContentList.cpp
@@ -254,19 +254,6 @@ const nsCacheableFuncStringContentList::ContentListType
   nsCacheableFuncStringHTMLCollection::sType = nsCacheableFuncStringContentList::eHTMLCollection;
 #endif
 
-JSObject*
-nsCacheableFuncStringNodeList::WrapObject(JSContext *cx, JS::Handle<JSObject*> aGivenProto)
-{
-  return NodeListBinding::Wrap(cx, this, aGivenProto);
-}
-
-
-JSObject*
-nsCacheableFuncStringHTMLCollection::WrapObject(JSContext *cx, JS::Handle<JSObject*> aGivenProto)
-{
-  return HTMLCollectionBinding::Wrap(cx, this, aGivenProto);
-}
-
 // Hashtable for storing nsCacheableFuncStringContentList
 static PLDHashTable* gFuncStringContentListHashTable;
 
@@ -379,6 +366,7 @@ NS_GetFuncStringHTMLCollection(nsINode* aRootNode,
                                                                        aString);
 }
 
+//-----------------------------------------------------
 // nsContentList implementation
 
 nsContentList::nsContentList(nsINode* aRootNode,
@@ -660,7 +648,7 @@ nsContentList::AttributeChanged(nsIDocument *aDocument, Element* aElement,
                                 const nsAttrValue* aOldValue)
 {
   NS_PRECONDITION(aElement, "Must have a content node to work with");
-  
+
   if (!mFunc || !mFuncMayDependOnAttr || mState == LIST_DIRTY ||
       !MayContainRelevantNodes(aElement->GetParentNode()) ||
       !nsContentUtils::IsInSameAnonymousTree(mRootNode, aElement)) {
@@ -806,7 +794,7 @@ nsContentList::ContentInserted(nsIDocument *aDocument,
 
   ASSERT_IN_SYNC;
 }
- 
+
 void
 nsContentList::ContentRemoved(nsIDocument *aDocument,
                               nsIContent* aContainer,
@@ -1075,3 +1063,128 @@ nsContentList::AssertInSync()
   NS_ASSERTION(cnt == mElements.Length(), "Too few elements");
 }
 #endif
+
+//-----------------------------------------------------
+// nsCacheableFuncStringNodeList
+
+JSObject*
+nsCacheableFuncStringNodeList::WrapObject(JSContext *cx, JS::Handle<JSObject*> aGivenProto)
+{
+  return NodeListBinding::Wrap(cx, this, aGivenProto);
+}
+
+//-----------------------------------------------------
+// nsCacheableFuncStringHTMLCollection
+
+JSObject*
+nsCacheableFuncStringHTMLCollection::WrapObject(JSContext *cx, JS::Handle<JSObject*> aGivenProto)
+{
+  return HTMLCollectionBinding::Wrap(cx, this, aGivenProto);
+}
+
+//-----------------------------------------------------
+// nsLabelsNodeList
+
+JSObject*
+nsLabelsNodeList::WrapObject(JSContext *cx, JS::Handle<JSObject*> aGivenProto)
+{
+  return NodeListBinding::Wrap(cx, this, aGivenProto);
+}
+
+void
+nsLabelsNodeList::AttributeChanged(nsIDocument* aDocument, Element* aElement,
+                                   int32_t aNameSpaceID, nsIAtom* aAttribute,
+                                   int32_t aModType,
+                                   const nsAttrValue* aOldValue)
+{
+  MOZ_ASSERT(aElement, "Must have a content node to work with");
+  if (mState == LIST_DIRTY ||
+      !nsContentUtils::IsInSameAnonymousTree(mRootNode, aElement)) {
+    return;
+  }
+
+  // We need to handle input type changes to or from "hidden".
+  if (aElement->IsHTMLElement(nsGkAtoms::input) &&
+      aAttribute == nsGkAtoms::type && aNameSpaceID == kNameSpaceID_None) {
+    SetDirty();
+    return;
+  }
+}
+
+void
+nsLabelsNodeList::ContentAppended(nsIDocument* aDocument,
+                                  nsIContent* aContainer,
+                                  nsIContent* aFirstNewContent,
+                                  int32_t aNewIndexInContainer)
+{
+  // If a labelable element is moved to outside or inside of
+  // nested associated labels, we're gonna have to modify
+  // the content list.
+  if (mState != LIST_DIRTY ||
+      nsContentUtils::IsInSameAnonymousTree(mRootNode, aContainer)) {
+    SetDirty();
+    return;
+  }
+}
+
+void
+nsLabelsNodeList::ContentInserted(nsIDocument* aDocument,
+                                  nsIContent* aContainer,
+                                  nsIContent* aChild,
+                                  int32_t aIndexInContainer)
+{
+  // If a labelable element is moved to outside or inside of
+  // nested associated labels, we're gonna have to modify
+  // the content list.
+  if (mState != LIST_DIRTY ||
+      nsContentUtils::IsInSameAnonymousTree(mRootNode, aChild)) {
+    SetDirty();
+    return;
+  }
+}
+
+void
+nsLabelsNodeList::ContentRemoved(nsIDocument* aDocument,
+                                 nsIContent* aContainer,
+                                 nsIContent* aChild,
+                                 int32_t aIndexInContainer,
+                                 nsIContent* aPreviousSibling)
+{
+  // If a labelable element is removed, we're gonna have to clean
+  // the content list.
+  if (mState != LIST_DIRTY ||
+      nsContentUtils::IsInSameAnonymousTree(mRootNode, aChild)) {
+    SetDirty();
+    return;
+  }
+}
+
+void
+nsLabelsNodeList::MaybeResetRoot(nsINode* aRootNode)
+{
+  MOZ_ASSERT(aRootNode, "Must have root");
+  if (mRootNode == aRootNode) {
+    return;
+  }
+
+  if (mRootNode) {
+    mRootNode->RemoveMutationObserver(this);
+  }
+  mRootNode = aRootNode;
+  mRootNode->AddMutationObserver(this);
+  SetDirty();
+}
+
+void
+nsLabelsNodeList::PopulateSelf(uint32_t aNeededLength)
+{
+  MOZ_ASSERT(mRootNode, "Must have root");
+
+  // Start searching at the root.
+  nsINode* cur = mRootNode;
+  if (mElements.IsEmpty() && cur->IsElement() && Match(cur->AsElement())) {
+    mElements.AppendElement(cur->AsElement());
+  }
+
+  nsContentList::PopulateSelf(aNeededLength);
+}
diff --git a/dom/base/nsContentList.h b/dom/base/nsContentList.h
index 3878074b2..83d27da95 100644
--- a/dom/base/nsContentList.h
+++ b/dom/base/nsContentList.h
@@ -371,9 +371,9 @@ protected:
    * traversed the whole document (or both).
    *
    * @param aNeededLength the length the list should have when we are
-   *        done (unless it exhausts the document)   
+   *        done (unless it exhausts the document)
    */
-  void PopulateSelf(uint32_t aNeededLength);
+  virtual void PopulateSelf(uint32_t aNeededLength);
 
   /**
    * @param  aContainer a content node which must be a descendant of
@@ -584,4 +584,40 @@ public:
 #endif
 };
 
+class nsLabelsNodeList final : public nsContentList
+{
+public:
+  nsLabelsNodeList(nsINode* aRootNode,
+                   nsContentListMatchFunc aFunc,
+                   nsContentListDestroyFunc aDestroyFunc,
+                   void* aData)
+    : nsContentList(aRootNode, aFunc, aDestroyFunc, aData)
+  {
+  }
+
+  NS_DECL_NSIMUTATIONOBSERVER_ATTRIBUTECHANGED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTAPPENDED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTINSERTED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTREMOVED
+
+  virtual JSObject* WrapObject(JSContext *cx, JS::Handle<JSObject*> aGivenProto) override;
+
+ /**
+  * Reset root, mutation observer, and clear content list
+  * if the root has been changed.
+  *
+  * @param aRootNode The node under which to limit our search.
+  */
+  void MaybeResetRoot(nsINode* aRootNode);
+
+private:
+ /**
+  * Start searching at the last one if we already have nodes, otherwise
+  * start searching at the root.
+  *
+  * @param aNeededLength The list of length should have when we are
+  *                      done (unless it exhausts the document).
+  */
+  void PopulateSelf(uint32_t aNeededLength) override;
+};
 #endif // nsContentList_h___
diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index 91427fabb..e4ae7ede8 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -526,6 +526,7 @@ GK_ATOM(keytext, "keytext")
 GK_ATOM(keyup, "keyup")
 GK_ATOM(kind, "kind")
 GK_ATOM(label, "label")
+GK_ATOM(labels, "labels")
 GK_ATOM(lang, "lang")
 GK_ATOM(language, "language")
 GK_ATOM(last, "last")
diff --git a/dom/base/test/test_bug1375050.html b/dom/base/test/test_bug1375050.html
new file mode 100644
index 000000000..b91b859d0
--- /dev/null
+++ b/dom/base/test/test_bug1375050.html
@@ -0,0 +1,33 @@
+<!DOCTYPE HTML>

+<html>

+<!--

+https://bugzilla.mozilla.org/show_bug.cgi?id=1375050

+-->

+<head>

+  <meta charset="utf-8">

+  <title>Test for Bug 1375050</title>

+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>

+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>

+  <script type="application/javascript">

+      try { o1 = document.createElement('input');  } catch(e) { console.log(e); };

+      try { o2 = document.createElement('col');  } catch(e) { console.log(e); };

+      try { o4 = document.createRange(); } catch(e) { console.log(e); };

+      try { document.documentElement.appendChild(o1); } catch(e) { console.log(e); };

+      try { for (let p in o1) { let x = o1[p] }; } catch(e) { console.log(e); };

+      try { o4.selectNode(o1); } catch(e) { console.log(e); };

+      try { o6 = document.createComment(" x"); } catch(e) { console.log(e); }

+      try { o4.surroundContents(o6); } catch(e) { console.log(e); }

+      try { o7 = document.implementation.createDocument('', '', null).adoptNode(o1); } catch(e) {  console.log(e);};

+      try { o2.appendChild(o1); } catch(e) { console.log(e); };

+      ok(true, "Didn't crash.");

+  </script>

+</head>

+<body>

+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1375050">Mozilla Bug 1375050</a>

+<p id="display"></p>

+<div id="content" style="display: none">

+</div>

+<pre id="test">

+</pre>

+</body>

+</html>

diff --git a/dom/html/HTMLInputElement.cpp b/dom/html/HTMLInputElement.cpp
index 78f74ae0c..d46eccdbc 100644
--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -8800,6 +8800,16 @@ HTMLInputElement::GetWebkitEntries(nsTArray<RefPtr<FileSystemEntry>>& aSequence)
   aSequence.AppendElements(mEntries);
 }
 
+already_AddRefed<nsINodeList>
+HTMLInputElement::GetLabels()
+{
+  if (!IsLabelable()) {
+    return nullptr;
+  }
+
+  return nsGenericHTMLElement::Labels();
+}
+
 } // namespace dom
 } // namespace mozilla
 
diff --git a/dom/html/HTMLInputElement.h b/dom/html/HTMLInputElement.h
index e5d670e08..9ca876aee 100644
--- a/dom/html/HTMLInputElement.h
+++ b/dom/html/HTMLInputElement.h
@@ -704,6 +704,8 @@ public:
 
   // XPCOM GetCustomVisibility() is OK
 
+  already_AddRefed<nsINodeList> GetLabels();
+
   // XPCOM Select() is OK
 
   Nullable<int32_t> GetSelectionStart(ErrorResult& aRv);
diff --git a/dom/html/HTMLLabelElement.cpp b/dom/html/HTMLLabelElement.cpp
index c1d22b0a6..d1c037336 100644
--- a/dom/html/HTMLLabelElement.cpp
+++ b/dom/html/HTMLLabelElement.cpp
@@ -14,6 +14,7 @@
 #include "nsFocusManager.h"
 #include "nsIDOMMouseEvent.h"
 #include "nsQueryObject.h"
+#include "mozilla/dom/ShadowRoot.h"
 
 // construction, destruction
 
@@ -268,17 +269,23 @@ HTMLLabelElement::GetLabeledElement() const
     return GetFirstLabelableDescendant();
   }
 
-  // We have a @for. The id has to be linked to an element in the same document
+  // We have a @for. The id has to be linked to an element in the same tree
   // and this element should be a labelable form control.
-  //XXXsmaug It is unclear how this should work in case the element is in
-  //         Shadow DOM.
-  //         See https://www.w3.org/Bugs/Public/show_bug.cgi?id=26365.
-  nsIDocument* doc = GetUncomposedDoc();
-  if (!doc) {
-    return nullptr;
+  nsINode* root = SubtreeRoot();
+  ShadowRoot* shadow = ShadowRoot::FromNode(root);
+  Element* element = nullptr;
+
+  if (shadow) {
+    element = shadow->GetElementById(elementId);
+  } else {
+    nsIDocument* doc = GetUncomposedDoc();
+    if (doc) {
+      element = doc->GetElementById(elementId);
+    } else {
+      element = nsContentUtils::MatchElementId(root->AsContent(), elementId);
+    }
   }
 
-  Element* element = doc->GetElementById(elementId);
   if (element && element->IsLabelable()) {
     return static_cast<nsGenericHTMLElement*>(element);
   }
diff --git a/dom/html/nsGenericHTMLElement.cpp b/dom/html/nsGenericHTMLElement.cpp
index d75001a83..2f890325a 100644
--- a/dom/html/nsGenericHTMLElement.cpp
+++ b/dom/html/nsGenericHTMLElement.cpp
@@ -108,6 +108,7 @@
 #include "mozilla/StyleSetHandle.h"
 #include "mozilla/StyleSetHandleInlines.h"
 #include "ReferrerPolicy.h"
+#include "mozilla/dom/HTMLLabelElement.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
@@ -493,6 +494,14 @@ nsGenericHTMLElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
     }
   }
 
+  // We need to consider a labels element is moved to another subtree
+  // with different root, it needs to update labels list and its root
+  // as well.
+  nsDOMSlots* slots = GetExistingDOMSlots();
+  if (slots && slots->mLabelsList) {
+    slots->mLabelsList->MaybeResetRoot(SubtreeRoot());
+  }
+
   return rv;
 }
 
@@ -513,6 +522,13 @@ nsGenericHTMLElement::UnbindFromTree(bool aDeep, bool aNullParent)
     }
   }
 
+  // We need to consider a labels element is removed from tree,
+  // it needs to update labels list and its root as well.
+  nsDOMSlots* slots = GetExistingDOMSlots();
+  if (slots && slots->mLabelsList) {
+    slots->mLabelsList->MaybeResetRoot(SubtreeRoot());
+  }
+
   nsStyledElement::UnbindFromTree(aDeep, aNullParent);
 }
 
@@ -1701,6 +1717,30 @@ nsGenericHTMLElement::IsLabelable() const
   return IsAnyOfHTMLElements(nsGkAtoms::progress, nsGkAtoms::meter);
 }
 
+/* static */ bool
+nsGenericHTMLElement::MatchLabelsElement(Element* aElement, int32_t aNamespaceID,
+                                         nsIAtom* aAtom, void* aData)
+{
+  HTMLLabelElement* element = HTMLLabelElement::FromContent(aElement);
+  return element && element->GetControl() == aData;
+}
+
+already_AddRefed<nsINodeList>
+nsGenericHTMLElement::Labels()
+{
+  MOZ_ASSERT(IsLabelable(),
+             "Labels() only allow labelable elements to use it.");
+  nsDOMSlots* slots = DOMSlots();
+
+  if (!slots->mLabelsList) {
+    slots->mLabelsList = new nsLabelsNodeList(SubtreeRoot(), MatchLabelsElement,
+                                              nullptr, this);
+  }
+
+  RefPtr<nsLabelsNodeList> labels = slots->mLabelsList;
+  return labels.forget();
+}
+
 bool
 nsGenericHTMLElement::IsInteractiveHTMLContent(bool aIgnoreTabindex) const
 {
diff --git a/dom/html/nsGenericHTMLElement.h b/dom/html/nsGenericHTMLElement.h
index 3cca41c3d..0635c27e1 100644
--- a/dom/html/nsGenericHTMLElement.h
+++ b/dom/html/nsGenericHTMLElement.h
@@ -834,6 +834,12 @@ public:
   }
 
   virtual bool IsLabelable() const override;
+
+  static bool MatchLabelsElement(Element* aElement, int32_t aNamespaceID,
+                                 nsIAtom* aAtom, void* aData);
+
+  already_AddRefed<nsINodeList> Labels();
+
   virtual bool IsInteractiveHTMLContent(bool aIgnoreTabindex) const override;
 
   static bool TouchEventsEnabled(JSContext* /* unused */, JSObject* /* unused */);
diff --git a/dom/html/test/forms/test_button_attributes_reflection.html b/dom/html/test/forms/test_button_attributes_reflection.html
index 26858e939..4e702b3ac 100644
--- a/dom/html/test/forms/test_button_attributes_reflection.html
+++ b/dom/html/test/forms/test_button_attributes_reflection.html
@@ -128,9 +128,12 @@ is(typeof(document.createElement("button").setCustomValidity), "function",
    "button.setCustomValidity should be a function");
 
 // .labels
-todo("labels" in document.createElement("button"),
-     "button.labels isn't implemented yet");
-
+ok("labels" in document.createElement("button"),
+   "button.labels should be an IDL attribute of the button element");
+is(typeof(document.createElement("button").labels), "object",
+   "button.labels should be an object");
+ok(document.createElement("button").labels instanceof NodeList,
+   "button.labels sohuld be an instance of NodeList");
 </script>
 </pre>
 </body>
diff --git a/dom/webidl/HTMLButtonElement.webidl b/dom/webidl/HTMLButtonElement.webidl
index c50e09ae0..579efa39c 100644
--- a/dom/webidl/HTMLButtonElement.webidl
+++ b/dom/webidl/HTMLButtonElement.webidl
@@ -44,6 +44,5 @@ interface HTMLButtonElement : HTMLElement {
   boolean reportValidity();
   void setCustomValidity(DOMString error);
 
-// Not yet implemented:
-//  readonly attribute NodeList labels;
+  readonly attribute NodeList labels;
 };
diff --git a/dom/webidl/HTMLInputElement.webidl b/dom/webidl/HTMLInputElement.webidl
index d3d537f84..050d19510 100644
--- a/dom/webidl/HTMLInputElement.webidl
+++ b/dom/webidl/HTMLInputElement.webidl
@@ -111,7 +111,7 @@ interface HTMLInputElement : HTMLElement {
   boolean reportValidity();
   void setCustomValidity(DOMString error);
 
-  // Bug 850365 readonly attribute NodeList labels;
+  readonly attribute NodeList? labels;
 
   void select();
 
diff --git a/dom/webidl/HTMLMeterElement.webidl b/dom/webidl/HTMLMeterElement.webidl
index 1f80764e9..104e00353 100644
--- a/dom/webidl/HTMLMeterElement.webidl
+++ b/dom/webidl/HTMLMeterElement.webidl
@@ -26,8 +26,5 @@ interface HTMLMeterElement : HTMLElement {
            [SetterThrows]
            attribute double optimum;
 
-  /**
-   * The labels attribute will be done with bug 556743.
-   */
-  //readonly attribute NodeList labels;
+           readonly attribute NodeList labels;
 };
diff --git a/dom/webidl/HTMLOutputElement.webidl b/dom/webidl/HTMLOutputElement.webidl
index 05dcf1800..d0e4ecbe6 100644
--- a/dom/webidl/HTMLOutputElement.webidl
+++ b/dom/webidl/HTMLOutputElement.webidl
@@ -33,6 +33,5 @@ interface HTMLOutputElement : HTMLElement {
   boolean reportValidity();
   void setCustomValidity(DOMString error);
 
-// Not yet implemented (bug 556743).
-//  readonly attribute NodeList labels;
+  readonly attribute NodeList labels;
 };
diff --git a/dom/webidl/HTMLProgressElement.webidl b/dom/webidl/HTMLProgressElement.webidl
index 3d1000d22..028728e22 100644
--- a/dom/webidl/HTMLProgressElement.webidl
+++ b/dom/webidl/HTMLProgressElement.webidl
@@ -17,9 +17,5 @@ interface HTMLProgressElement : HTMLElement {
            [SetterThrows]
            attribute double max;
   readonly attribute double position;
-
-  /**
-   * The labels attribute will be done with bug 567740.
-   */
-  //readonly attribute NodeList labels;
+  readonly attribute NodeList labels;
 };
diff --git a/dom/webidl/HTMLSelectElement.webidl b/dom/webidl/HTMLSelectElement.webidl
index 74fc7b2cf..b18ca3634 100644
--- a/dom/webidl/HTMLSelectElement.webidl
+++ b/dom/webidl/HTMLSelectElement.webidl
@@ -53,7 +53,7 @@ interface HTMLSelectElement : HTMLElement {
   boolean reportValidity();
   void setCustomValidity(DOMString error);
 
-// NYI:  readonly attribute NodeList labels;
+  readonly attribute NodeList labels;
 
   // https://www.w3.org/Bugs/Public/show_bug.cgi?id=20720
   void remove();
diff --git a/dom/webidl/HTMLTextAreaElement.webidl b/dom/webidl/HTMLTextAreaElement.webidl
index b1005ed42..4df687a0b 100644
--- a/dom/webidl/HTMLTextAreaElement.webidl
+++ b/dom/webidl/HTMLTextAreaElement.webidl
@@ -57,7 +57,7 @@ interface HTMLTextAreaElement : HTMLElement {
   boolean reportValidity();
   void setCustomValidity(DOMString error);
 
-  // readonly attribute NodeList labels;
+  readonly attribute NodeList labels;
 
   void select();
   [Throws]