Quelle Element.cpp Sprache: C

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*
* Base class for all element classes; this provides an implementation
* of DOM Core's Element, implements nsIContent, provides
* utility methods for subclasses, and so forth.
*/

#include "mozilla/dom/Element.h"
#include "mozilla/dom/ElementInlines.h"

#include <cstddef>
#include <inttypes.h>
#include <initializer_list>
#include <utility>
#include "DOMMatrix.h"
#include "ExpandedPrincipal.h"
#include "PresShellInlines.h"
#include "jsapi.h"
#include "mozAutoDocUpdate.h"
#include "mozilla/AnimationComparator.h"
#include "mozilla/AnimationTarget.h"
#include "mozilla/AsyncEventDispatcher.h"
#include "mozilla/CORSMode.h"
#include "mozilla/Components.h"
#include "mozilla/ComputedStyle.h"
#include "mozilla/ContentEvents.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/DeclarationBlock.h"
#include "mozilla/EditorBase.h"
#include "mozilla/EffectCompositor.h"
#include "mozilla/EffectSet.h"
#include "mozilla/ElementAnimationData.h"
#include "mozilla/ErrorResult.h"
#include "mozilla/EventDispatcher.h"
#include "mozilla/EventListenerManager.h"
#include "mozilla/EventStateManager.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/FullscreenChange.h"
#include "mozilla/HTMLEditor.h"
#include "mozilla/InternalMutationEvent.h"
#include "mozilla/Likely.h"
#include "mozilla/LinkedList.h"
#include "mozilla/LookAndFeel.h"
#include "mozilla/MappedDeclarationsBuilder.h"
#include "mozilla/Maybe.h"
#include "mozilla/MouseEvents.h"
#include "mozilla/NotNull.h"
#include "mozilla/PointerLockManager.h"
#include "mozilla/PresShell.h"
#include "mozilla/PresShellForwards.h"
#include "mozilla/ReflowOutput.h"
#include "mozilla/RefPtr.h"
#include "mozilla/RelativeTo.h"
#include "mozilla/ScrollContainerFrame.h"
#include "mozilla/ScrollTypes.h"
#include "mozilla/ServoStyleConsts.h"
#include "mozilla/ServoStyleConstsInlines.h"
#include "mozilla/SizeOfState.h"
#include "mozilla/SourceLocation.h"
#include "mozilla/StaticAnalysisFunctions.h"
#include "mozilla/StaticPrefs_dom.h"
#include "mozilla/StaticPrefs_full_screen_api.h"
#include "mozilla/StaticString.h"
#include "mozilla/TextControlElement.h"
#include "mozilla/TextEditor.h"
#include "mozilla/TextEvents.h"
#include "mozilla/Try.h"
#include "mozilla/TypedEnumBits.h"
#include "mozilla/Unused.h"
#include "mozilla/dom/AnimatableBinding.h"
#include "mozilla/dom/Animation.h"
#include "mozilla/dom/Attr.h"
#include "mozilla/dom/BindContext.h"
#include "mozilla/dom/BindingDeclarations.h"
#include "mozilla/dom/CloseWatcher.h"
#include "mozilla/dom/CustomElementRegistry.h"
#include "mozilla/dom/CSPViolationData.h"
#include "mozilla/dom/DOMRect.h"
#include "mozilla/dom/DirectionalityUtils.h"
#include "mozilla/dom/Document.h"
#include "mozilla/dom/DocumentFragment.h"
#include "mozilla/dom/DocumentInlines.h"
#include "mozilla/dom/DocumentTimeline.h"
#include "mozilla/dom/ElementBinding.h"
#include "mozilla/dom/Flex.h"
#include "mozilla/dom/FragmentOrElement.h"
#include "mozilla/dom/FromParser.h"
#include "mozilla/dom/Grid.h"
#include "mozilla/dom/HTMLDivElement.h"
#include "mozilla/dom/HTMLElement.h"
#include "mozilla/dom/HTMLParagraphElement.h"
#include "mozilla/dom/HTMLPreElement.h"
#include "mozilla/dom/HTMLSpanElement.h"
#include "mozilla/dom/HTMLTableCellElement.h"
#include "mozilla/dom/HTMLTemplateElement.h"
#include "mozilla/dom/KeyframeAnimationOptionsBinding.h"
#include "mozilla/dom/KeyframeEffect.h"
#include "mozilla/dom/MouseEvent.h"
#include "mozilla/dom/MouseEventBinding.h"
#include "mozilla/dom/MutationEventBinding.h"
#include "mozilla/dom/MutationObservers.h"
#include "mozilla/dom/NodeInfo.h"
#include "mozilla/dom/nsCSPUtils.h"
#include "mozilla/dom/PointerEventHandler.h"
#include "mozilla/dom/Promise.h"
#include "mozilla/dom/Sanitizer.h"
#include "mozilla/dom/SVGElement.h"
#include "mozilla/dom/ScriptLoader.h"
#include "mozilla/dom/ShadowRoot.h"
#include "mozilla/dom/Text.h"
#include "mozilla/dom/TrustedHTML.h"
#include "mozilla/dom/TrustedTypesConstants.h"
#include "mozilla/dom/TrustedTypeUtils.h"
#include "mozilla/dom/UnbindContext.h"
#include "mozilla/dom/ViewTransition.h"
#include "mozilla/dom/WindowBinding.h"
#include "mozilla/dom/XULCommandEvent.h"
#include "mozilla/dom/nsCSPContext.h"
#include "mozilla/gfx/BasePoint.h"
#include "mozilla/gfx/BaseRect.h"
#include "mozilla/gfx/BaseSize.h"
#include "mozilla/gfx/Matrix.h"
#include "mozilla/widget/Screen.h"
#include "nsAtom.h"
#include "nsAttrName.h"
#include "nsAttrValueInlines.h"
#include "nsAttrValueOrString.h"
#include "nsBaseHashtable.h"
#include "nsBlockFrame.h"
#include "nsCOMPtr.h"
#include "nsContentUtils.h"
#include "nsCSSPseudoElements.h"
#include "nsCompatibility.h"
#include "nsContainerFrame.h"
#include "nsContentList.h"
#include "nsContentListDeclarations.h"
#include "nsCoord.h"
#include "nsDOMAttributeMap.h"
#include "nsDOMCSSAttrDeclaration.h"
#include "nsDOMMutationObserver.h"
#include "nsDOMString.h"
#include "nsDOMStringMap.h"
#include "nsDOMTokenList.h"
#include "nsDocShell.h"
#include "nsError.h"
#include "nsFlexContainerFrame.h"
#include "nsFocusManager.h"
#include "nsFrameState.h"
#include "nsGenericHTMLElement.h"
#include "nsGkAtoms.h"
#include "nsGridContainerFrame.h"
#include "nsIContentSecurityPolicy.h"
#include "nsIAutoCompletePopup.h"
#include "nsIBrowser.h"
#include "nsIContentInlines.h"
#include "nsIDOMXULButtonElement.h"
#include "nsIDOMXULContainerElement.h"
#include "nsIDOMXULControlElement.h"
#include "nsIDOMXULMenuListElement.h"
#include "nsIDOMXULMultSelectCntrlEl.h"
#include "nsIDOMXULRadioGroupElement.h"
#include "nsIDOMXULRelatedElement.h"
#include "nsIDOMXULSelectCntrlEl.h"
#include "nsIDOMXULSelectCntrlItemEl.h"
#include "nsIDocShell.h"
#include "nsIFocusManager.h"
#include "nsIFrame.h"
#include "nsIGlobalObject.h"
#include "nsIIOService.h"
#include "nsIInterfaceRequestor.h"
#include "nsIMemoryReporter.h"
#include "nsIPrincipal.h"
#include "nsIScriptError.h"
#include "nsISpeculativeConnect.h"
#include "nsISupports.h"
#include "nsISupportsUtils.h"
#include "nsIURI.h"
#include "nsLayoutUtils.h"
#include "nsLineBox.h"
#include "nsLiteralString.h"
#include "nsNameSpaceManager.h"
#include "nsNodeInfoManager.h"
#include "nsPIDOMWindow.h"
#include "nsPoint.h"
#include "nsPresContext.h"
#include "nsQueryFrame.h"
#include "nsRefPtrHashtable.h"
#include "nsSize.h"
#include "nsString.h"
#include "nsStyleConsts.h"
#include "nsStyleStruct.h"
#include "nsStyledElement.h"
#include "nsTArray.h"
#include "nsTextNode.h"
#include "nsThreadUtils.h"
#include "nsViewManager.h"
#include "nsWindowSizes.h"

#include "nsXULElement.h"

#ifdef DEBUG
#  include "nsRange.h"
#endif

#ifdef ACCESSIBILITY
#  include "nsAccessibilityService.h"
#endif

using mozilla::gfx::Matrix4x4;

namespace mozilla::dom {

// Verify sizes of nodes. We use a template rather than a direct static
// assert so that the error message actually displays the sizes.
// On 32 bit systems the actual allocated size varies a bit between
// OSes/compilers.
//
// We need different numbers on certain build types to deal with the owning
// thread pointer that comes with the non-threadsafe refcount on
// nsIContent.
#ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
#  define EXTRA_DOM_NODE_BYTES 8
#else
#  define EXTRA_DOM_NODE_BYTES 0
#endif

#define ASSERT_NODE_SIZE(type, opt_size_64, opt_size_32)              \
  template <int a, int sizeOn64, int sizeOn32>                        \
  struct Check##type##Size {                                          \
    static_assert((sizeof(void*) == 8 && a == sizeOn64) ||            \
                      (sizeof(void*) == 4 && a <= sizeOn32),          \
                  "DOM size changed");                                \
  };                                                                  \
  Check##type##Size<sizeof(type), opt_size_64 + EXTRA_DOM_NODE_BYTES, \
                    opt_size_32 + EXTRA_DOM_NODE_BYTES>               \
      g##type##CES;

// Note that mozjemalloc uses a 16 byte quantum, so 64, 80 and 128 are
// bucket sizes.
ASSERT_NODE_SIZE(Element, 128, 80);
ASSERT_NODE_SIZE(HTMLDivElement, 128, 80);
ASSERT_NODE_SIZE(HTMLElement, 128, 80);
ASSERT_NODE_SIZE(HTMLParagraphElement, 128, 80);
ASSERT_NODE_SIZE(HTMLPreElement, 128, 80);
ASSERT_NODE_SIZE(HTMLSpanElement, 128, 80);
ASSERT_NODE_SIZE(HTMLTableCellElement, 128, 80);
ASSERT_NODE_SIZE(Text, 120, 80);

#undef ASSERT_NODE_SIZE
#undef EXTRA_DOM_NODE_BYTES

}  // namespace mozilla::dom

nsAtom* nsIContent::DoGetID() const {
  MOZ_ASSERT(HasID(), "Unexpected call");
  MOZ_ASSERT(IsElement(), "Only elements can have IDs");

  return AsElement()->GetParsedAttr(nsGkAtoms::id)->GetAtomValue();
}

nsIFrame* nsIContent::GetPrimaryFrame(mozilla::FlushType aType) {
  Document* doc = GetComposedDoc();
  if (!doc) {
    return nullptr;
  }

  // Cause a flush, so we get up-to-date frame information.
  if (aType != mozilla::FlushType::None) {
    doc->FlushPendingNotifications(aType);
  }

  auto* frame = GetPrimaryFrame();
  if (!frame) {
    return nullptr;
  }

  if (aType == mozilla::FlushType::Layout) {
    frame->PresShell()->EnsureReflowIfFrameHasHiddenContent(frame);
    frame = GetPrimaryFrame();
  }

  return frame;
}

namespace mozilla::dom {

const DOMTokenListSupportedToken Element::sSupportedBlockingValues[] = {
    "render", nullptr};

nsDOMAttributeMap* Element::Attributes() {
  nsDOMSlots* slots = DOMSlots();
  if (!slots->mAttributeMap) {
    slots->mAttributeMap = new nsDOMAttributeMap(this);
  }

  return slots->mAttributeMap;
}

void Element::SetPointerCapture(int32_t aPointerId, ErrorResult& aError) {
  if (OwnerDoc()->ShouldResistFingerprinting(RFPTarget::PointerId) &&
      aPointerId != PointerEventHandler::GetSpoofedPointerIdForRFP()) {
    aError.ThrowNotFoundError("Invalid pointer id");
    return;
  }
  const PointerInfo* pointerInfo =
      PointerEventHandler::GetPointerInfo(aPointerId);
  if (!pointerInfo) {
    aError.ThrowNotFoundError("Invalid pointer id");
    return;
  }
  if (!IsInComposedDoc()) {
    aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
    return;
  }
  if (OwnerDoc()->GetPointerLockElement()) {
    // Throw an exception 'InvalidStateError' while the page has a locked
    // element.
    aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
    return;
  }
  if (!pointerInfo->mActiveState ||
      pointerInfo->mActiveDocument != OwnerDoc()) {
    return;
  }
  PointerEventHandler::RequestPointerCaptureById(aPointerId, this);
}

void Element::ReleasePointerCapture(int32_t aPointerId, ErrorResult& aError) {
  if (OwnerDoc()->ShouldResistFingerprinting(RFPTarget::PointerId) &&
      aPointerId != PointerEventHandler::GetSpoofedPointerIdForRFP()) {
    aError.ThrowNotFoundError("Invalid pointer id");
    return;
  }
  if (!PointerEventHandler::GetPointerInfo(aPointerId)) {
    aError.ThrowNotFoundError("Invalid pointer id");
    return;
  }
  if (HasPointerCapture(aPointerId)) {
    PointerEventHandler::ReleasePointerCaptureById(aPointerId);
  }
}

bool Element::HasPointerCapture(long aPointerId) {
  PointerCaptureInfo* pointerCaptureInfo =
      PointerEventHandler::GetPointerCaptureInfo(aPointerId);
  if (pointerCaptureInfo && pointerCaptureInfo->mPendingElement == this) {
    return true;
  }
  return false;
}

const nsAttrValue* Element::GetSVGAnimatedClass() const {
  MOZ_ASSERT(MayHaveClass() && IsSVGElement(), "Unexpected call");
  return static_cast<const SVGElement*>(this)->GetAnimatedClassName();
}

NS_IMETHODIMP
Element::QueryInterface(REFNSIID aIID, void** aInstancePtr) {
  if (aIID.Equals(NS_GET_IID(Element))) {
    NS_ADDREF_THIS();
    *aInstancePtr = this;
    return NS_OK;
  }

  NS_ASSERTION(aInstancePtr, "QueryInterface requires a non-NULL destination!");
  nsresult rv = FragmentOrElement::QueryInterface(aIID, aInstancePtr);
  if (NS_SUCCEEDED(rv)) {
    return NS_OK;
  }

  return NS_NOINTERFACE;
}

void Element::NotifyStateChange(ElementState aStates) {
  MOZ_ASSERT(!aStates.IsEmpty());
  if (Document* doc = GetComposedDoc()) {
    nsAutoScriptBlocker scriptBlocker;
    doc->ElementStateChanged(this, aStates);
  }
}

}  // namespace mozilla::dom

void nsIContent::UpdateEditableState(bool aNotify) {
  if (IsInNativeAnonymousSubtree()) {
    // Don't propagate the editable flag into native anonymous subtrees.
    if (IsRootOfNativeAnonymousSubtree()) {
      return;
    }

    // We allow setting the flag on NAC (explicitly, see
    // nsTextControlFrame::CreateAnonymousContent for example), but not
    // unsetting it.
    //
    // Otherwise, just the act of binding the NAC subtree into our non-anonymous
    // parent would clear the flag, which is not good. As we shouldn't move NAC
    // around, this is fine.
    if (HasFlag(NODE_IS_EDITABLE)) {
      return;
    }
  }

  nsIContent* parent = GetParent();
  SetEditableFlag(parent && parent->HasFlag(NODE_IS_EDITABLE));
}

namespace mozilla::dom {

void Element::UpdateEditableState(bool aNotify) {
  nsIContent::UpdateEditableState(aNotify);
  UpdateReadOnlyState(aNotify);
}

bool Element::IsReadOnlyInternal() const { return !IsEditable(); }

void Element::UpdateReadOnlyState(bool aNotify) {
  auto oldState = State();
  if (IsReadOnlyInternal()) {
    RemoveStatesSilently(ElementState::READWRITE);
    AddStatesSilently(ElementState::READONLY);
  } else {
    RemoveStatesSilently(ElementState::READONLY);
    AddStatesSilently(ElementState::READWRITE);
  }
  if (!aNotify) {
    return;
  }
  const auto newState = State();
  if (newState != oldState) {
    NotifyStateChange(newState ^ oldState);
  }
}

Maybe<int32_t> Element::GetTabIndexAttrValue() {
  const nsAttrValue* attrVal = GetParsedAttr(nsGkAtoms::tabindex);
  if (attrVal && attrVal->Type() == nsAttrValue::eInteger) {
    return Some(attrVal->GetIntegerValue());
  }

  return Nothing();
}

int32_t Element::TabIndex() {
  Maybe<int32_t> attrVal = GetTabIndexAttrValue();
  if (attrVal.isSome()) {
    return attrVal.value();
  }

  return TabIndexDefault();
}

void Element::Focus(const FocusOptions& aOptions, CallerType aCallerType,
                    ErrorResult& aError) {
  const RefPtr<nsFocusManager> fm = nsFocusManager::GetFocusManager();
  if (MOZ_UNLIKELY(!fm)) {
    return;
  }
  const OwningNonNull<Element> kungFuDeathGrip(*this);
  // Also other browsers seem to have the hack to not re-focus (and flush) when
  // the element is already focused.
  // Until https://github.com/whatwg/html/issues/4512 is clarified, we'll
  // maintain interoperatibility by not re-focusing, independent of aOptions.
  // I.e., `focus({ preventScroll: true})` followed by `focus( { preventScroll:
  // false })` won't re-focus.
  if (fm->CanSkipFocus(this)) {
    fm->NotifyOfReFocus(kungFuDeathGrip);
    fm->NeedsFlushBeforeEventHandling(this);
    return;
  }
  uint32_t fmFlags = nsFocusManager::ProgrammaticFocusFlags(aOptions);
  if (aCallerType == CallerType::NonSystem) {
    fmFlags |= nsIFocusManager::FLAG_NONSYSTEMCALLER;
  }
  aError = fm->SetFocus(kungFuDeathGrip, fmFlags);
}

void Element::SetTabIndex(int32_t aTabIndex, mozilla::ErrorResult& aError) {
  nsAutoString value;
  value.AppendInt(aTabIndex);

  SetAttr(nsGkAtoms::tabindex, value, aError);
}

void Element::SetShadowRoot(ShadowRoot* aShadowRoot) {
  nsExtendedDOMSlots* slots = ExtendedDOMSlots();
  MOZ_ASSERT(!aShadowRoot || !slots->mShadowRoot,
             "We shouldn't clear the shadow root without unbind first");
  slots->mShadowRoot = aShadowRoot;
}

void Element::SetLastRememberedBSize(float aBSize) {
  ExtendedDOMSlots()->mLastRememberedBSize = Some(aBSize);
}

void Element::SetLastRememberedISize(float aISize) {
  ExtendedDOMSlots()->mLastRememberedISize = Some(aISize);
}

void Element::RemoveLastRememberedBSize() {
  if (nsExtendedDOMSlots* slots = GetExistingExtendedDOMSlots()) {
    slots->mLastRememberedBSize.reset();
  }
}

void Element::RemoveLastRememberedISize() {
  if (nsExtendedDOMSlots* slots = GetExistingExtendedDOMSlots()) {
    slots->mLastRememberedISize.reset();
  }
}

void Element::Blur(mozilla::ErrorResult& aError) {
  if (!ShouldBlur(this)) {
    return;
  }

  Document* doc = GetComposedDoc();
  if (!doc) {
    return;
  }

  if (nsCOMPtr<nsPIDOMWindowOuter> win = doc->GetWindow()) {
    if (RefPtr<nsFocusManager> fm = nsFocusManager::GetFocusManager()) {
      aError = fm->ClearFocus(win);
    }
  }
}

ElementState Element::StyleStateFromLocks() const {
  StyleStateLocks locksAndValues = LockedStyleStates();
  ElementState locks = locksAndValues.mLocks;
  ElementState values = locksAndValues.mValues;
  ElementState state = (mState & ~locks) | (locks & values);

  if (state.HasState(ElementState::VISITED)) {
    return state & ~ElementState::UNVISITED;
  }
  if (state.HasState(ElementState::UNVISITED)) {
    return state & ~ElementState::VISITED;
  }

  return state;
}

Element::StyleStateLocks Element::LockedStyleStates() const {
  StyleStateLocks* locks =
      static_cast<StyleStateLocks*>(GetProperty(nsGkAtoms::lockedStyleStates));
  if (locks) {
    return *locks;
  }
  return StyleStateLocks();
}

void Element::NotifyStyleStateChange(ElementState aStates) {
  if (RefPtr<Document> doc = GetComposedDoc()) {
    if (RefPtr<PresShell> presShell = doc->GetPresShell()) {
      nsAutoScriptBlocker scriptBlocker;
      presShell->ElementStateChanged(doc, this, aStates);
    }
  }
}

void Element::LockStyleStates(ElementState aStates, bool aEnabled) {
  StyleStateLocks* locks = new StyleStateLocks(LockedStyleStates());

  locks->mLocks |= aStates;
  if (aEnabled) {
    locks->mValues |= aStates;
  } else {
    locks->mValues &= ~aStates;
  }

  if (aStates.HasState(ElementState::VISITED)) {
    locks->mLocks &= ~ElementState::UNVISITED;
  }
  if (aStates.HasState(ElementState::UNVISITED)) {
    locks->mLocks &= ~ElementState::VISITED;
  }

  SetProperty(nsGkAtoms::lockedStyleStates, locks,
              nsINode::DeleteProperty<StyleStateLocks>);
  SetHasLockedStyleStates();

  NotifyStyleStateChange(aStates);
}

void Element::UnlockStyleStates(ElementState aStates) {
  StyleStateLocks* locks = new StyleStateLocks(LockedStyleStates());

  locks->mLocks &= ~aStates;

  if (locks->mLocks.IsEmpty()) {
    RemoveProperty(nsGkAtoms::lockedStyleStates);
    ClearHasLockedStyleStates();
    delete locks;
  } else {
    SetProperty(nsGkAtoms::lockedStyleStates, locks,
                nsINode::DeleteProperty<StyleStateLocks>);
  }

  NotifyStyleStateChange(aStates);
}

void Element::ClearStyleStateLocks() {
  StyleStateLocks locks = LockedStyleStates();

  RemoveProperty(nsGkAtoms::lockedStyleStates);
  ClearHasLockedStyleStates();

  NotifyStyleStateChange(locks.mLocks);
}

/* virtual */
nsINode* Element::GetScopeChainParent() const { return OwnerDoc(); }

JSObject* Element::WrapNode(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
  return Element_Binding::Wrap(aCx, this, aGivenProto);
}

nsDOMTokenList* Element::ClassList() {
  nsDOMSlots* slots = DOMSlots();
  if (!slots->mClassList) {
    slots->mClassList = new nsDOMTokenList(this, nsGkAtoms::_class);
  }
  return slots->mClassList;
}

nsDOMTokenList* Element::Part() {
  nsExtendedDOMSlots* slots = ExtendedDOMSlots();
  if (!slots->mPart) {
    slots->mPart = new nsDOMTokenList(this, nsGkAtoms::part);
  }
  return slots->mPart;
}

void Element::RecompileScriptEventListeners() {
  for (uint32_t i = 0, count = mAttrs.AttrCount(); i < count; ++i) {
    BorrowedAttrInfo attrInfo = mAttrs.AttrInfoAt(i);

    // Eventlistenener-attributes are always in the null namespace
    if (!attrInfo.mName->IsAtom()) {
      continue;
    }

    nsAtom* attr = attrInfo.mName->Atom();
    if (!IsEventAttributeName(attr)) {
      continue;
    }

    nsAutoString value;
    attrInfo.mValue->ToString(value);
    SetEventHandler(GetEventNameForAttr(attr), value, true);
  }
}

void Element::GetAttributeNames(nsTArray<nsString>& aResult) {
  uint32_t count = mAttrs.AttrCount();
  for (uint32_t i = 0; i < count; ++i) {
    const nsAttrName* name = mAttrs.AttrNameAt(i);
    name->GetQualifiedName(*aResult.AppendElement());
  }
}

already_AddRefed<nsIHTMLCollection> Element::GetElementsByTagName(
    const nsAString& aLocalName) {
  return NS_GetContentList(this, kNameSpaceID_Unknown, aLocalName);
}

ScrollContainerFrame* Element::GetScrollContainerFrame(nsIFrame** aFrame,
                                                       FlushType aFlushType) {
  nsIFrame* frame = GetPrimaryFrame(aFlushType);
  if (aFrame) {
    *aFrame = frame;
  }
  if (frame) {
    if (frame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
      // It's unclear what to return for SVG frames, so just return null.
      return nullptr;
    }

    if (ScrollContainerFrame* scrollContainerFrame =
            frame->GetScrollTargetFrame()) {
      MOZ_ASSERT(!OwnerDoc()->IsScrollingElement(this),
                 "How can we have a scroll container frame if we're the "
                 "scrollingElement for our document?");
      return scrollContainerFrame;
    }
  }

  Document* doc = OwnerDoc();
  // Note: This IsScrollingElement() call can flush frames, if we're the body of
  // a quirks mode document.
  const bool isScrollingElement = doc->IsScrollingElement(this);
  if (isScrollingElement) {
    // Our scroll info should map to the root scroll container frame if there is
    // one.
    if (PresShell* presShell = doc->GetPresShell()) {
      if (ScrollContainerFrame* rootScrollContainerFrame =
              presShell->GetRootScrollContainerFrame()) {
        if (aFrame) {
          *aFrame = rootScrollContainerFrame;
        }
        return rootScrollContainerFrame;
      }
    }
  }
  if (aFrame) {
    // Re-get *aFrame if the caller asked for it, because that frame flush can
    // kill it.
    *aFrame = GetPrimaryFrame(FlushType::None);
  }
  return nullptr;
}

bool Element::CheckVisibility(const CheckVisibilityOptions& aOptions) {
  nsIFrame* f =
      GetPrimaryFrame(aOptions.mFlush ? FlushType::Frames : FlushType::None);
  if (!f) {
    // 1. If this does not have an associated box, return false.
    return false;
  }

  EnumSet includeContentVisibility = {
      nsIFrame::IncludeContentVisibility::Hidden};
  if (aOptions.mContentVisibilityAuto) {
    includeContentVisibility += nsIFrame::IncludeContentVisibility::Auto;
  }
  // Steps 2 and 5
  if (f->IsHiddenByContentVisibilityOnAnyAncestor(includeContentVisibility)) {
    // 2. If a shadow-including ancestor of this has content-visibility: hidden,
    // return false.
    // 5. If a shadow-including ancestor of this skips its content due to
    // has content-visibility: auto, return false.
    return false;
  }

  if ((aOptions.mOpacityProperty || aOptions.mCheckOpacity) &&
      f->Style()->IsInOpacityZeroSubtree()) {
    // 3. If the checkOpacity dictionary member of options is true, and this, or
    // a shadow-including ancestor of this, has a computed opacity value of 0,
    // return false.
    return false;
  }

  if ((aOptions.mVisibilityProperty || aOptions.mCheckVisibilityCSS) &&
      !f->StyleVisibility()->IsVisible()) {
    // 4. If the checkVisibilityCSS dictionary member of options is true, and
    // this is invisible, return false.
    return false;
  }

  // 6. Return true
  return true;
}

void Element::ScrollIntoView(const BooleanOrScrollIntoViewOptions& aObject) {
  if (aObject.IsScrollIntoViewOptions()) {
    return ScrollIntoView(aObject.GetAsScrollIntoViewOptions());
  }

  MOZ_DIAGNOSTIC_ASSERT(aObject.IsBoolean());

  ScrollIntoViewOptions options;
  if (aObject.GetAsBoolean()) {
    options.mBlock = ScrollLogicalPosition::Start;
    options.mInline = ScrollLogicalPosition::Nearest;
  } else {
    options.mBlock = ScrollLogicalPosition::End;
    options.mInline = ScrollLogicalPosition::Nearest;
  }
  return ScrollIntoView(options);
}

void Element::ScrollIntoView(const ScrollIntoViewOptions& aOptions) {
  Document* document = GetComposedDoc();
  if (!document) {
    return;
  }

  // Get the presentation shell
  RefPtr<PresShell> presShell = document->GetPresShell();
  if (!presShell) {
    return;
  }

  const auto ToWhereToScroll =
      [](ScrollLogicalPosition aPosition) -> WhereToScroll {
    switch (aPosition) {
      case ScrollLogicalPosition::Start:
        return WhereToScroll::Start;
      case ScrollLogicalPosition::Center:
        return WhereToScroll::Center;
      case ScrollLogicalPosition::End:
        return WhereToScroll::End;
      case ScrollLogicalPosition::Nearest:
        break;
    }
    return WhereToScroll::Nearest;
  };

  const auto block = ToWhereToScroll(aOptions.mBlock);
  const auto inline_ = ToWhereToScroll(aOptions.mInline);

  ScrollFlags scrollFlags =
      ScrollFlags::ScrollOverflowHidden | ScrollFlags::TriggeredByScript;
  if (aOptions.mBehavior == ScrollBehavior::Smooth) {
    scrollFlags |= ScrollFlags::ScrollSmooth;
  } else if (aOptions.mBehavior == ScrollBehavior::Auto) {
    scrollFlags |= ScrollFlags::ScrollSmoothAuto;
  }

  // TODO: Propagate whether the axes are logical or not down (via scrollflags).
  presShell->ScrollContentIntoView(
      this, ScrollAxis(block, WhenToScroll::Always),
      ScrollAxis(inline_, WhenToScroll::Always), scrollFlags);
}

void Element::ScrollTo(double aXScroll, double aYScroll) {
  ScrollToOptions options;
  options.mLeft.Construct(aXScroll);
  options.mTop.Construct(aYScroll);
  ScrollTo(options);
}

void Element::ScrollTo(const ScrollToOptions& aOptions) {
  // When the scroll top is 0, we don't need to flush layout to scroll to that
  // point; we know 0 is always in range.  At least we think so...  But we do
  // need to flush frames so we ensure we find the right scrollable frame if
  // there is one. If it's nonzero, we need to flush layout because we need to
  // figure out what our real scrollTopMax is.
  //
  // If we have a left value, we can't assume things based on it's value,
  // depending on our direction and layout 0 may or may not be in our scroll
  // range.  So we need to flush layout no matter what then.
  const bool needsLayoutFlush =
      aOptions.mLeft.WasPassed() ||
      (aOptions.mTop.WasPassed() && aOptions.mTop.Value() != 0.0);

  nsIFrame* frame;
  ScrollContainerFrame* sf = GetScrollContainerFrame(
      &frame, needsLayoutFlush ? FlushType::Layout : FlushType::Frames);
  if (!sf) {
    return;
  }
  CSSIntPoint scrollPos = sf->GetRoundedScrollPositionCSSPixels();
  if (aOptions.mLeft.WasPassed()) {
    scrollPos.x = int32_t(mozilla::ToZeroIfNonfinite(
        frame->Style()->EffectiveZoom().Zoom(aOptions.mLeft.Value())));
  }
  if (aOptions.mTop.WasPassed()) {
    scrollPos.y = int32_t(mozilla::ToZeroIfNonfinite(
        frame->Style()->EffectiveZoom().Zoom(aOptions.mTop.Value())));
  }
  ScrollMode scrollMode = sf->IsSmoothScroll(aOptions.mBehavior)
                              ? ScrollMode::SmoothMsd
                              : ScrollMode::Instant;
  sf->ScrollToCSSPixels(scrollPos, scrollMode);
}

void Element::ScrollBy(double aXScrollDif, double aYScrollDif) {
  ScrollToOptions options;
  options.mLeft.Construct(aXScrollDif);
  options.mTop.Construct(aYScrollDif);
  ScrollBy(options);
}

void Element::ScrollBy(const ScrollToOptions& aOptions) {
  nsIFrame* frame;
  ScrollContainerFrame* sf = GetScrollContainerFrame(&frame);
  if (!sf) {
    return;
  }

  CSSIntPoint scrollDelta;
  if (aOptions.mLeft.WasPassed()) {
    scrollDelta.x = int32_t(mozilla::ToZeroIfNonfinite(
        frame->Style()->EffectiveZoom().Zoom(aOptions.mLeft.Value())));
  }

  if (aOptions.mTop.WasPassed()) {
    scrollDelta.y = int32_t(mozilla::ToZeroIfNonfinite(
        frame->Style()->EffectiveZoom().Zoom(aOptions.mTop.Value())));
  }

  auto scrollMode = sf->IsSmoothScroll(aOptions.mBehavior)
                        ? ScrollMode::SmoothMsd
                        : ScrollMode::Instant;
  sf->ScrollByCSSPixels(scrollDelta, scrollMode);
}

int32_t Element::ScrollTop() {
  return CSSPixel::FromAppUnitsRounded(GetScrollOrigin().y);
}

void Element::SetScrollTop(int32_t aScrollTop) {
  ScrollToOptions options;
  options.mTop.Construct(aScrollTop);
  ScrollTo(options);
}

int32_t Element::ScrollLeft() {
  return CSSPixel::FromAppUnitsRounded(GetScrollOrigin().x);
}

void Element::SetScrollLeft(int32_t aScrollLeft) {
  ScrollToOptions options;
  options.mLeft.Construct(aScrollLeft);
  ScrollTo(options);
}

void Element::MozScrollSnap() {
  if (ScrollContainerFrame* sf =
          GetScrollContainerFrame(nullptr, FlushType::None)) {
    sf->ScrollSnap();
  }
}

nsRect Element::GetScrollRange() {
  nsIFrame* frame;
  ScrollContainerFrame* sf = GetScrollContainerFrame(&frame);
  if (!sf) {
    return nsRect();
  }
  return frame->Style()->EffectiveZoom().Unzoom(sf->GetScrollRange());
}

int32_t Element::ScrollTopMin() {
  return CSSPixel::FromAppUnitsRounded(GetScrollRange().Y());
}

int32_t Element::ScrollTopMax() {
  return CSSPixel::FromAppUnitsRounded(GetScrollRange().YMost());
}

int32_t Element::ScrollLeftMin() {
  return CSSPixel::FromAppUnitsRounded(GetScrollRange().X());
}

int32_t Element::ScrollLeftMax() {
  return CSSPixel::FromAppUnitsRounded(GetScrollRange().XMost());
}

static nsSize GetScrollRectSizeForOverflowVisibleFrame(nsIFrame* aFrame) {
  if (!aFrame || aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
    return nsSize();
  }

  // This matches WebKit and Blink, which in turn (apparently, according to
  // their source) matched old IE.
  const nsRect paddingRect = aFrame->GetPaddingRectRelativeToSelf();
  const nsRect overflowRect = [&] {
    OverflowAreas overflowAreas(paddingRect, paddingRect);
    // Add the scrollable overflow areas of children (if any) to the
    // paddingRect, as if aFrame was a scrolled frame. It's important to start
    // with the paddingRect, otherwise if there are no children the overflow
    // rect will be 0,0,0,0 which will force the point 0,0 to be included in the
    // final rect.
    aFrame->UnionChildOverflow(overflowAreas, /* aAsIfScrolled = */ true);
    // Make sure that an empty padding-rect's edges are included, by adding
    // the padding-rect in again with UnionEdges.
    return overflowAreas.ScrollableOverflow().UnionEdges(paddingRect);
  }();

  auto directions =
      ScrollContainerFrame::ComputePerAxisScrollDirections(aFrame);
  const nscoord height = directions.mToBottom
                             ? overflowRect.YMost() - paddingRect.Y()
                             : paddingRect.YMost() - overflowRect.Y();
  const nscoord width = directions.mToRight
                            ? overflowRect.XMost() - paddingRect.X()
                            : paddingRect.XMost() - overflowRect.X();
  return nsSize(width, height);
}

nsSize Element::GetScrollSize() {
  nsIFrame* frame;
  nsSize size;
  if (ScrollContainerFrame* sf = GetScrollContainerFrame(&frame)) {
    size = sf->GetScrollRange().Size() + sf->GetScrollPortRect().Size();
  } else {
    size = GetScrollRectSizeForOverflowVisibleFrame(frame);
  }
  if (!frame) {
    return size;
  }
  return frame->Style()->EffectiveZoom().Unzoom(size);
}

nsPoint Element::GetScrollOrigin() {
  nsIFrame* frame;
  ScrollContainerFrame* sf = GetScrollContainerFrame(&frame);
  if (!sf) {
    return nsPoint();
  }
  return frame->Style()->EffectiveZoom().Unzoom(sf->GetScrollPosition());
}

int32_t Element::ScrollHeight() {
  return nsPresContext::AppUnitsToIntCSSPixels(GetScrollSize().height);
}

int32_t Element::ScrollWidth() {
  return nsPresContext::AppUnitsToIntCSSPixels(GetScrollSize().width);
}

nsRect Element::GetClientAreaRect() {
  Document* doc = OwnerDoc();
  nsPresContext* presContext = doc->GetPresContext();

  // We can avoid a layout flush if this is the scrolling element of the
  // document, we have overlay scrollbars, and we aren't embedded in another
  // document
  if (presContext && presContext->UseOverlayScrollbars() &&
      !doc->StyleOrLayoutObservablyDependsOnParentDocumentLayout() &&
      doc->IsScrollingElement(this)) {
    if (PresShell* presShell = doc->GetPresShell()) {
      // Ensure up to date dimensions, but don't reflow
      if (RefPtr<nsViewManager> viewManager = presShell->GetViewManager()) {
        viewManager->FlushDelayedResize();
      }
      return nsRect(nsPoint(), presContext->GetVisibleArea().Size());
    }
  }

  nsIFrame* frame;
  if (ScrollContainerFrame* sf = GetScrollContainerFrame(&frame)) {
    nsRect scrollPort = sf->GetScrollPortRect();

    if (!sf->IsRootScrollFrameOfDocument()) {
      MOZ_ASSERT(frame);
      // We want the offset to be relative to `frame`, not `sf`... Except for
      // the root scroll frame, which is an ancestor of frame rather than a
      // descendant and thus this wouldn't particularly make sense.
      if (frame != sf) {
        scrollPort.MoveBy(sf->GetOffsetTo(frame));
      }
    }

    // The scroll port value might be expanded to the minimum scale size, we
    // should limit the size to the ICB in such cases.
    scrollPort.SizeTo(sf->GetLayoutSize());
    return frame->Style()->EffectiveZoom().Unzoom(scrollPort);
  }

  if (frame &&
      // The display check is OK even though we're not looking at the style
      // frame, because the style frame only differs from "frame" for tables,
      // and table wrappers have the same display as the table itself.
      (!frame->StyleDisplay()->IsInlineFlow() || frame->IsReplaced())) {
    // Special case code to make client area work even when there isn't
    // a scroll view, see bug 180552, bug 227567.
    return frame->Style()->EffectiveZoom().Unzoom(
        frame->GetPaddingRect() - frame->GetPositionIgnoringScrolling());
  }

  // SVG nodes reach here and just return 0
  return nsRect();
}

int32_t Element::ScreenX() {
  nsIFrame* frame = GetPrimaryFrame(FlushType::Layout);
  return frame ? frame->GetScreenRect().x : 0;
}

int32_t Element::ScreenY() {
  nsIFrame* frame = GetPrimaryFrame(FlushType::Layout);
  return frame ? frame->GetScreenRect().y : 0;
}

already_AddRefed<nsIScreen> Element::GetScreen() {
  // Flush layout to guarantee that frames are created if needed, and preserve
  // behavior.
  Unused << GetPrimaryFrame(FlushType::Frames);
  if (nsIWidget* widget = nsContentUtils::WidgetForContent(this)) {
    return widget->GetWidgetScreen();
  }
  return nullptr;
}

double Element::CurrentCSSZoom() {
  nsIFrame* f = GetPrimaryFrame(FlushType::Frames);
  if (!f) {
    return 1.0;
  }
  return f->Style()->EffectiveZoom().ToFloat();
}

already_AddRefed<DOMRect> Element::GetBoundingClientRect() {
  RefPtr<DOMRect> rect = new DOMRect(ToSupports(OwnerDoc()));

  nsIFrame* frame = GetPrimaryFrame(FlushType::Layout);
  if (!frame) {
    // display:none, perhaps? Return the empty rect
    return rect.forget();
  }

  rect->SetLayoutRect(frame->GetBoundingClientRect());
  return rect.forget();
}

already_AddRefed<DOMRectList> Element::GetClientRects() {
  RefPtr<DOMRectList> rectList = new DOMRectList(this);

  nsIFrame* frame = GetPrimaryFrame(FlushType::Layout);
  if (!frame) {
    // display:none, perhaps? Return an empty list
    return rectList.forget();
  }

  nsLayoutUtils::RectListBuilder builder(rectList);
  nsLayoutUtils::GetAllInFlowRects(
      frame, nsLayoutUtils::GetContainingBlockForClientRect(frame), &builder,
      nsLayoutUtils::GetAllInFlowRectsFlag::AccountForTransforms);
  return rectList.forget();
}

const DOMTokenListSupportedToken Element::sAnchorAndFormRelValues[] = {
    "noreferrer", "noopener", "opener", nullptr};

// https://html.spec.whatwg.org/multipage/urls-and-fetching.html#lazy-loading-attribute
static constexpr nsAttrValue::EnumTable kLoadingTable[] = {
    {"eager", Element::Loading::Eager},
    {"lazy", Element::Loading::Lazy},
    {nullptr, 0}};

void Element::GetLoading(nsAString& aValue) const {
  GetEnumAttr(nsGkAtoms::loading, kLoadingTable[0].tag, aValue);
}

bool Element::ParseLoadingAttribute(const nsAString& aValue,
                                    nsAttrValue& aResult) {
  return aResult.ParseEnumValue(aValue, kLoadingTable,
                                /* aCaseSensitive = */ false, kLoadingTable);
}

Element::Loading Element::LoadingState() const {
  const nsAttrValue* val = mAttrs.GetAttr(nsGkAtoms::loading);
  if (!val) {
    return Loading::Eager;
  }
  return static_cast<Loading>(val->GetEnumValue());
}

//----------------------------------------------------------------------

void Element::AddToIdTable(nsAtom* aId) {
  NS_ASSERTION(HasID(), "Node doesn't have an ID?");
  if (IsInShadowTree()) {
    ShadowRoot* containingShadow = GetContainingShadow();
    containingShadow->AddToIdTable(this, aId);
  } else {
    Document* doc = GetUncomposedDoc();
    if (doc && !IsInNativeAnonymousSubtree()) {
      doc->AddToIdTable(this, aId);
    }
  }
}

void Element::RemoveFromIdTable() {
  if (!HasID()) {
    return;
  }

  nsAtom* id = DoGetID();
  if (IsInShadowTree()) {
    ShadowRoot* containingShadow = GetContainingShadow();
    // Check for containingShadow because it may have
    // been deleted during unlinking.
    if (containingShadow) {
      containingShadow->RemoveFromIdTable(this, id);
    }
  } else {
    Document* doc = GetUncomposedDoc();
    if (doc && !IsInNativeAnonymousSubtree()) {
      doc->RemoveFromIdTable(this, id);
    }
  }
}

void Element::SetSlot(const nsAString& aName, ErrorResult& aError) {
  aError = SetAttr(kNameSpaceID_None, nsGkAtoms::slot, aName, true);
}

void Element::GetSlot(nsAString& aName) { GetAttr(nsGkAtoms::slot, aName); }

// https://dom.spec.whatwg.org/#dom-element-shadowroot
ShadowRoot* Element::GetShadowRootByMode() const {
  /**
   * 1. Let shadow be context object's shadow root.
   * 2. If shadow is null or its mode is "closed", then return null.
   */
  ShadowRoot* shadowRoot = GetShadowRoot();
  if (!shadowRoot || shadowRoot->IsClosed()) {
    return nullptr;
  }

  /**
   * 3. Return shadow.
   */
  return shadowRoot;
}

bool Element::CanAttachShadowDOM() const {
  /**
   * If context object's namespace is not the HTML namespace,
   * return false.
   *
   * Deviate from the spec here to allow shadow dom attachement to
   * XUL elements.
   */
  if (!IsHTMLElement() &&
      !(IsXULElement() &&
        nsContentUtils::AllowXULXBLForPrincipal(NodePrincipal()))) {
    return false;
  }

  /**
   * If context object's local name is not
   *    a valid custom element name, "article", "aside", "blockquote",
   *    "body", "div", "footer", "h1", "h2", "h3", "h4", "h5", "h6",
   *    "header", "main" "nav", "p", "section", "search", or "span",
   *  return false.
   */
  nsAtom* nameAtom = NodeInfo()->NameAtom();
  uint32_t namespaceID = NodeInfo()->NamespaceID();
  if (!(nsContentUtils::IsCustomElementName(nameAtom, namespaceID) ||
        nameAtom == nsGkAtoms::article || nameAtom == nsGkAtoms::aside ||
        nameAtom == nsGkAtoms::blockquote || nameAtom == nsGkAtoms::body ||
        nameAtom == nsGkAtoms::div || nameAtom == nsGkAtoms::footer ||
        nameAtom == nsGkAtoms::h1 || nameAtom == nsGkAtoms::h2 ||
        nameAtom == nsGkAtoms::h3 || nameAtom == nsGkAtoms::h4 ||
        nameAtom == nsGkAtoms::h5 || nameAtom == nsGkAtoms::h6 ||
        nameAtom == nsGkAtoms::header || nameAtom == nsGkAtoms::main ||
        nameAtom == nsGkAtoms::nav || nameAtom == nsGkAtoms::p ||
        nameAtom == nsGkAtoms::section || nameAtom == nsGkAtoms::search ||
        nameAtom == nsGkAtoms::span)) {
    return false;
  }

  /**
   * 3. If context object’s local name is a valid custom element name, or
   *    context object’s is value is not null, then:
   *    If definition is not null and definition’s disable shadow is true, then
   *    return false.
   */
  // It will always have CustomElementData when the element is a valid custom
  // element or has is value.
  if (CustomElementData* ceData = GetCustomElementData()) {
    CustomElementDefinition* definition = ceData->GetCustomElementDefinition();
    // If the definition is null, the element possible hasn't yet upgraded.
    // Fallback to use LookupCustomElementDefinition to find its definition.
    if (!definition) {
      definition = nsContentUtils::LookupCustomElementDefinition(
          NodeInfo()->GetDocument(), nameAtom, namespaceID,
          ceData->GetCustomElementType());
    }

    if (definition && definition->mDisableShadow) {
      return false;
    }
  }

  return true;
}

// https://dom.spec.whatwg.org/#dom-element-attachshadow
already_AddRefed<ShadowRoot> Element::AttachShadow(const ShadowRootInit& aInit,
                                                   ErrorResult& aError) {
  /**
   * Step 1, 2, and 3.
   */
  if (!CanAttachShadowDOM()) {
    aError.ThrowNotSupportedError("Unable to attach ShadowDOM");
    return nullptr;
  }

  /**
   * 4. If element is a shadow host, then:
   */
  if (RefPtr<ShadowRoot> root = GetShadowRoot()) {
    /**
     *  1. Let currentShadowRoot be element’s shadow root.
     *
     *  2. If any of the following are true:
     *      currentShadowRoot’s declarative is false; or
     *      currentShadowRoot’s mode is not mode,
     *  then throw a "NotSupportedError" DOMException.
     */
    if (!root->IsDeclarative() || root->Mode() != aInit.mMode) {
      aError.ThrowNotSupportedError(
          "Unable to re-attach to existing ShadowDOM");
      return nullptr;
    }
    /**
     * 3. Otherwise:
     *      1. Remove all of currentShadowRoot’s children, in tree order.
     *      2. Set currentShadowRoot’s declarative to false.
     *      3. Return.
     */
    root->ReplaceChildren(nullptr, aError);
    root->SetIsDeclarative(ShadowRootDeclarative::No);
    return root.forget();
  }

  if (StaticPrefs::dom_webcomponents_shadowdom_report_usage()) {
    OwnerDoc()->ReportShadowDOMUsage();
  }

  return AttachShadowWithoutNameChecks(
      aInit.mMode, DelegatesFocus(aInit.mDelegatesFocus), aInit.mSlotAssignment,
      ShadowRootClonable(aInit.mClonable),
      ShadowRootSerializable(aInit.mSerializable));
}

already_AddRefed<ShadowRoot> Element::AttachShadowWithoutNameChecks(
    ShadowRootMode aMode, DelegatesFocus aDelegatesFocus,
    SlotAssignmentMode aSlotAssignment, ShadowRootClonable aClonable,
    ShadowRootSerializable aSerializable) {
  nsAutoScriptBlocker scriptBlocker;

  auto* nim = mNodeInfo->NodeInfoManager();
  RefPtr<mozilla::dom::NodeInfo> nodeInfo =
      nim->GetNodeInfo(nsGkAtoms::documentFragmentNodeName, nullptr,
                       kNameSpaceID_None, DOCUMENT_FRAGMENT_NODE);

  // If there are no children, the flat tree is not changing due to the presence
  // of the shadow root, so we don't need to invalidate style / layout.
  //
  // This is a minor optimization, but also works around nasty stuff like
  // bug 1397876.
  if (Document* doc = GetComposedDoc()) {
    if (PresShell* presShell = doc->GetPresShell()) {
      presShell->ShadowRootWillBeAttached(*this);
    }
  }

  /**
   * 5. Let shadow be a new shadow root whose node document is
   *    context object's node document, host is context object,
   *    and mode is init's mode.
   */
  RefPtr<ShadowRoot> shadowRoot = new (nim)
      ShadowRoot(this, aMode, aDelegatesFocus, aSlotAssignment, aClonable,
                 aSerializable, ShadowRootDeclarative::No, nodeInfo.forget());

  if (NodeOrAncestorHasDirAuto()) {
    shadowRoot->SetAncestorHasDirAuto();
  }

  /**
   * 7. If this’s custom element state is "precustomized" or "custom", then set
   *    shadow’s available to element internals to true.
   */
  CustomElementData* ceData = GetCustomElementData();
  if (ceData && (ceData->mState == CustomElementData::State::ePrecustomized ||
                 ceData->mState == CustomElementData::State::eCustom)) {
    shadowRoot->SetAvailableToElementInternals();
  }

  /**
   * 9. Set context object's shadow root to shadow.
   */
  SetShadowRoot(shadowRoot);

  // Dispatch a "shadowrootattached" event for devtools if needed.
  if (MOZ_UNLIKELY(
          nim->GetDocument()->DevToolsAnonymousAndShadowEventsEnabled())) {
    AsyncEventDispatcher* dispatcher = new AsyncEventDispatcher(
        this, u"shadowrootattached"_ns, CanBubble::eYes,
        ChromeOnlyDispatch::eYes, Composed::eYes);
    dispatcher->PostDOMEvent();
  }

  const LinkedList<AbstractRange>* ranges =
      GetExistingClosestCommonInclusiveAncestorRanges();
  if (ranges) {
    for (const AbstractRange* range : *ranges) {
      if (range->MayCrossShadowBoundary()) {
        MOZ_ASSERT(range->IsDynamicRange());
        CrossShadowBoundaryRange* crossBoundaryRange =
            range->AsDynamicRange()->GetCrossShadowBoundaryRange();
        MOZ_ASSERT(crossBoundaryRange);
        // We may have previously selected this node before it
        // becomes a shadow host, so we need to reset the values
        // in RangeBoundaries to accommodate the change.
        crossBoundaryRange->NotifyNodeBecomesShadowHost(this);
      }
    }
  }
  /**
   * 10. Return shadow.
   */
  return shadowRoot.forget();
}

void Element::AttachAndSetUAShadowRoot(NotifyUAWidgetSetup aNotify,
                                       DelegatesFocus aDelegatesFocus) {
  MOZ_DIAGNOSTIC_ASSERT(!CanAttachShadowDOM(),
                        "Cannot be used to attach UI shadow DOM");
  if (OwnerDoc()->IsStaticDocument()) {
    return;
  }

  if (!GetShadowRoot()) {
    RefPtr<ShadowRoot> shadowRoot =
        AttachShadowWithoutNameChecks(ShadowRootMode::Closed, aDelegatesFocus);
    shadowRoot->SetIsUAWidget();
  }

  MOZ_ASSERT(GetShadowRoot()->IsUAWidget());
  if (aNotify == NotifyUAWidgetSetup::Yes) {
    NotifyUAWidgetSetupOrChange();
  }
}

void Element::NotifyUAWidgetSetupOrChange() {
  MOZ_ASSERT(IsInComposedDoc());
  Document* doc = OwnerDoc();
  if (doc->IsStaticDocument()) {
    return;
  }

  // Schedule a runnable, ensure the event dispatches before
  // returning to content script.
  // This event cause UA Widget to construct or cause onchange callback
  // of existing UA Widget to run; dispatching this event twice should not cause
  // UA Widget to re-init.
  nsContentUtils::AddScriptRunner(NS_NewRunnableFunction(
      "Element::NotifyUAWidgetSetupOrChange::UAWidgetSetupOrChange",
      [self = RefPtr<Element>(this), doc = RefPtr<Document>(doc)]() {
        nsContentUtils::DispatchChromeEvent(doc, self,
                                            u"UAWidgetSetupOrChange"_ns,
                                            CanBubble::eYes, Cancelable::eNo);
      }));
}

void Element::NotifyUAWidgetTeardown(UnattachShadowRoot aUnattachShadowRoot) {
  MOZ_ASSERT(IsInComposedDoc());
  if (!GetShadowRoot()) {
    return;
  }
  MOZ_ASSERT(GetShadowRoot()->IsUAWidget());
  if (aUnattachShadowRoot == UnattachShadowRoot::Yes) {
    UnattachShadow();
  }

  Document* doc = OwnerDoc();
  if (doc->IsStaticDocument()) {
    return;
  }

  // The runnable will dispatch an event to tear down UA Widget.
  nsContentUtils::AddScriptRunner(NS_NewRunnableFunction(
      "Element::NotifyUAWidgetTeardownAndUnattachShadow::UAWidgetTeardown",
      [self = RefPtr<Element>(this), doc = RefPtr<Document>(doc)]() {
        // Bail out if the element is being collected by CC
        bool hasHadScriptObject = true;
        nsIScriptGlobalObject* scriptObject =
            doc->GetScriptHandlingObject(hasHadScriptObject);
        if (!scriptObject && hasHadScriptObject) {
          return;
        }

        Unused << nsContentUtils::DispatchChromeEvent(
            doc, self, u"UAWidgetTeardown"_ns, CanBubble::eYes,
            Cancelable::eNo);
      }));
}

void Element::UnattachShadow() {
  RefPtr<ShadowRoot> shadowRoot = GetShadowRoot();
  if (!shadowRoot) {
    return;
  }

  nsAutoScriptBlocker scriptBlocker;

  if (RefPtr<Document> doc = GetComposedDoc()) {
    if (PresShell* presShell = doc->GetPresShell()) {
      presShell->DestroyFramesForAndRestyle(this);
#ifdef ACCESSIBILITY
      // We need to notify the accessibility service here explicitly because,
      // even though we're going to reconstruct the _host_, the shadow root and
      // its children are never really going to come back. We could plumb that
      // further down to DestroyFramesForAndRestyle and add a new flag to
      // nsCSSFrameConstructor::ContentRemoved or such, but this seems simpler
      // instead.
      if (nsAccessibilityService* accService = GetAccService()) {
        accService->ContentRemoved(presShell, shadowRoot);
      }
#endif
    }
    // ContentRemoved doesn't really run script in the cases we care about (it
    // can only call ClearFocus when removing iframes and so on...)
    [&]() MOZ_CAN_RUN_SCRIPT_BOUNDARY {
      if (RefPtr<nsFocusManager> fm = nsFocusManager::GetFocusManager()) {
        fm->ContentRemoved(doc, shadowRoot);
      }
    }();
  }
  MOZ_ASSERT(!GetPrimaryFrame());

  shadowRoot->Unattach();
  SetShadowRoot(nullptr);
}

void Element::GetAttribute(const nsAString& aName, DOMString& aReturn) {
  const nsAttrValue* val = mAttrs.GetAttr(
      aName,
      IsHTMLElement() && IsInHTMLDocument() ? eIgnoreCase : eCaseMatters);
  if (val) {
    val->ToString(aReturn);
  } else {
    aReturn.SetNull();
  }
}

bool Element::ToggleAttribute(const nsAString& aName,
                              const Optional<bool>& aForce,
                              nsIPrincipal* aTriggeringPrincipal,
                              ErrorResult& aError) {
  aError = nsContentUtils::CheckQName(aName, false);
  if (aError.Failed()) {
    return false;
  }

  nsAutoString nameToUse;
  const nsAttrName* name = InternalGetAttrNameFromQName(aName, &nameToUse);
  if (!name) {
    if (aForce.WasPassed() && !aForce.Value()) {
      return false;
    }
    RefPtr<nsAtom> nameAtom = NS_AtomizeMainThread(nameToUse);
    if (!nameAtom) {
      aError.Throw(NS_ERROR_OUT_OF_MEMORY);
      return false;
    }
    aError = SetAttr(kNameSpaceID_None, nameAtom, u""_ns, aTriggeringPrincipal,
                     true);
    return true;
  }
  if (aForce.WasPassed() && aForce.Value()) {
    return true;
  }
  // Hold a strong reference here so that the atom or nodeinfo doesn't go
  // away during UnsetAttr. If it did UnsetAttr would be left with a
  // dangling pointer as argument without knowing it.
  nsAttrName tmp(*name);

  aError = UnsetAttr(name->NamespaceID(), name->LocalName(), true);
  return false;
}

void Element::SetAttribute(const nsAString& aName, const nsAString& aValue,
                           nsIPrincipal* aTriggeringPrincipal,
                           ErrorResult& aError) {
  aError = nsContentUtils::CheckQName(aName, false);
  if (aError.Failed()) {
    return;
  }

  nsAutoString nameToUse;
  const nsAttrName* name = InternalGetAttrNameFromQName(aName, &nameToUse);
  if (!name) {
    RefPtr<nsAtom> nameAtom = NS_AtomizeMainThread(nameToUse);
    if (!nameAtom) {
      aError.Throw(NS_ERROR_OUT_OF_MEMORY);
      return;
    }
    aError = SetAttr(kNameSpaceID_None, nameAtom, aValue, aTriggeringPrincipal,
                     true);
    return;
  }

  aError = SetAttr(name->NamespaceID(), name->LocalName(), name->GetPrefix(),
                   aValue, aTriggeringPrincipal, true);
}

void Element::RemoveAttribute(const nsAString& aName, ErrorResult& aError) {
  const nsAttrName* name = InternalGetAttrNameFromQName(aName);

  if (!name) {
    // If there is no canonical nsAttrName for this attribute name, then the
    // attribute does not exist and we can't get its namespace ID and
    // local name below, so we return early.
    return;
  }

  // Hold a strong reference here so that the atom or nodeinfo doesn't go
  // away during UnsetAttr. If it did UnsetAttr would be left with a
  // dangling pointer as argument without knowing it.
  nsAttrName tmp(*name);

  aError = UnsetAttr(name->NamespaceID(), name->LocalName(), true);
}

Attr* Element::GetAttributeNode(const nsAString& aName) {
  return Attributes()->GetNamedItem(aName);
}

already_AddRefed<Attr> Element::SetAttributeNode(Attr& aNewAttr,
                                                 ErrorResult& aError) {
  return Attributes()->SetNamedItemNS(aNewAttr, aError);
}

already_AddRefed<Attr> Element::RemoveAttributeNode(Attr& aAttribute,
                                                    ErrorResult& aError) {
  Element* elem = aAttribute.GetElement();
  if (elem != this) {
    aError.Throw(NS_ERROR_DOM_NOT_FOUND_ERR);
    return nullptr;
  }

  nsAutoString nameSpaceURI;
  aAttribute.NodeInfo()->GetNamespaceURI(nameSpaceURI);
  return Attributes()->RemoveNamedItemNS(
      nameSpaceURI, aAttribute.NodeInfo()->LocalName(), aError);
}

void Element::GetAttributeNS(const nsAString& aNamespaceURI,
                             const nsAString& aLocalName, nsAString& aReturn) {
  int32_t nsid = nsNameSpaceManager::GetInstance()->GetNameSpaceID(
      aNamespaceURI, nsContentUtils::IsChromeDoc(OwnerDoc()));

  if (nsid == kNameSpaceID_Unknown) {
    // Unknown namespace means no attribute.
    SetDOMStringToNull(aReturn);
    return;
  }

  RefPtr<nsAtom> name = NS_AtomizeMainThread(aLocalName);
  bool hasAttr = GetAttr(nsid, name, aReturn);
  if (!hasAttr) {
    SetDOMStringToNull(aReturn);
  }
}

void Element::SetAttributeNS(const nsAString& aNamespaceURI,
                             const nsAString& aQualifiedName,
                             const nsAString& aValue,
                             nsIPrincipal* aTriggeringPrincipal,
                             ErrorResult& aError) {
  RefPtr<mozilla::dom::NodeInfo> ni;
  aError = nsContentUtils::GetNodeInfoFromQName(
      aNamespaceURI, aQualifiedName, mNodeInfo->NodeInfoManager(),
      ATTRIBUTE_NODE, getter_AddRefs(ni));
  if (aError.Failed()) {
    return;
  }

  aError = SetAttr(ni->NamespaceID(), ni->NameAtom(), ni->GetPrefixAtom(),
                   aValue, aTriggeringPrincipal, true);
}

already_AddRefed<nsIPrincipal> Element::CreateDevtoolsPrincipal() {
  // Return an ExpandedPrincipal that subsumes this Element's Principal,
  // and expands this Element's CSP to allow the actions that devtools
  // needs to perform.
  AutoTArray<nsCOMPtr<nsIPrincipal>, 1> allowList = {NodePrincipal()};
  RefPtr<ExpandedPrincipal> dtPrincipal = ExpandedPrincipal::Create(
      allowList, NodePrincipal()->OriginAttributesRef());

  if (nsIContentSecurityPolicy* csp = GetCsp()) {
    RefPtr<nsCSPContext> dtCsp = new nsCSPContext();
    dtCsp->InitFromOther(static_cast<nsCSPContext*>(csp));
    dtCsp->SetSkipAllowInlineStyleCheck(true);

    dtPrincipal->SetCsp(dtCsp);
  }

  return dtPrincipal.forget();
}

void Element::SetAttribute(
    const nsAString& aName,
    const TrustedHTMLOrTrustedScriptOrTrustedScriptURLOrString& aValue,
    nsIPrincipal* aTriggeringPrincipal, ErrorResult& aError) {
  aError = nsContentUtils::CheckQName(aName, false);
  if (aError.Failed()) {
    return;
  }

  nsAutoString nameToUse;
  const nsAttrName* name = InternalGetAttrNameFromQName(aName, &nameToUse);
  if (!name) {
    RefPtr<nsAtom> nameAtom = NS_AtomizeMainThread(nameToUse);
    Maybe<nsAutoString> compliantStringHolder;
    const nsAString* compliantString =
        TrustedTypeUtils::GetTrustedTypesCompliantAttributeValue(
            *this, nameAtom, kNameSpaceID_None, aValue, compliantStringHolder,
            aError);
    if (aError.Failed()) {
      return;
    }
    aError = SetAttr(kNameSpaceID_None, nameAtom, *compliantString,
                     aTriggeringPrincipal, true);
    return;
  }

  Maybe<nsAutoString> compliantStringHolder;
  RefPtr<nsAtom> attributeName = name->LocalName();
  nsMutationGuard guard;
  const nsAString* compliantString =
      TrustedTypeUtils::GetTrustedTypesCompliantAttributeValue(
          *this, attributeName, name->NamespaceID(), aValue,
          compliantStringHolder, aError);
  if (aError.Failed()) {
    return;
  }
  if (!guard.Mutated(0)) {
    aError = SetAttr(name->NamespaceID(), name->LocalName(), name->GetPrefix(),
                     *compliantString, aTriggeringPrincipal, true);
    return;
  }

  // GetTrustedTypesCompliantAttributeValue may have modified mAttrs and made
  // the result of InternalGetAttrNameFromQName above invalid. It may now return
  // a different value, perhaps a nullptr. To be safe, just call the version of
  // Element::SetAttribute accepting a string value.
  SetAttribute(aName, *compliantString, aTriggeringPrincipal, aError);
}

void Element::SetAttributeNS(
    const nsAString& aNamespaceURI, const nsAString& aQualifiedName,
    const TrustedHTMLOrTrustedScriptOrTrustedScriptURLOrString& aValue,
    nsIPrincipal* aTriggeringPrincipal, ErrorResult& aError) {
  RefPtr<mozilla::dom::NodeInfo> ni;
  aError = nsContentUtils::GetNodeInfoFromQName(
      aNamespaceURI, aQualifiedName, mNodeInfo->NodeInfoManager(),
      ATTRIBUTE_NODE, getter_AddRefs(ni));
  if (aError.Failed()) {
    return;
  }

  Maybe<nsAutoString> compliantStringHolder;
  RefPtr<nsAtom> attributeName = ni->NameAtom();
  const nsAString* compliantString =
      TrustedTypeUtils::GetTrustedTypesCompliantAttributeValue(
          *this, attributeName, ni->NamespaceID(), aValue,
          compliantStringHolder, aError);
  if (aError.Failed()) {
    return;
  }
  aError = SetAttr(ni->NamespaceID(), ni->NameAtom(), ni->GetPrefixAtom(),
                   *compliantString, aTriggeringPrincipal, true);
}

void Element::SetAttributeDevtools(const nsAString& aName,
                                   const nsAString& aValue,
                                   ErrorResult& aError) {
  // Run this through SetAttribute with a devtools-ready principal.
  RefPtr<nsIPrincipal> dtPrincipal = CreateDevtoolsPrincipal();
  SetAttribute(aName, aValue, dtPrincipal, aError);
}

void Element::SetAttributeDevtoolsNS(const nsAString& aNamespaceURI,
                                     const nsAString& aLocalName,
                                     const nsAString& aValue,
                                     ErrorResult& aError) {
  // Run this through SetAttributeNS with a devtools-ready principal.
  RefPtr<nsIPrincipal> dtPrincipal = CreateDevtoolsPrincipal();
  SetAttributeNS(aNamespaceURI, aLocalName, aValue, dtPrincipal, aError);
}

void Element::RemoveAttributeNS(const nsAString& aNamespaceURI,
                                const nsAString& aLocalName,
                                ErrorResult& aError) {
  RefPtr<nsAtom> name = NS_AtomizeMainThread(aLocalName);
  int32_t nsid = nsNameSpaceManager::GetInstance()->GetNameSpaceID(
      aNamespaceURI, nsContentUtils::IsChromeDoc(OwnerDoc()));

  if (nsid == kNameSpaceID_Unknown) {
    // If the namespace ID is unknown, it means there can't possibly be an
    // existing attribute. We would need a known namespace ID to pass into
    // UnsetAttr, so we return early if we don't have one.
    return;
  }

  aError = UnsetAttr(nsid, name, true);
}

Attr* Element::GetAttributeNodeNS(const nsAString& aNamespaceURI,
                                  const nsAString& aLocalName) {
  return GetAttributeNodeNSInternal(aNamespaceURI, aLocalName);
}

Attr* Element::GetAttributeNodeNSInternal(const nsAString& aNamespaceURI,
                                          const nsAString& aLocalName) {
  return Attributes()->GetNamedItemNS(aNamespaceURI, aLocalName);
}

already_AddRefed<Attr> Element::SetAttributeNodeNS(Attr& aNewAttr,
                                                   ErrorResult& aError) {
  return Attributes()->SetNamedItemNS(aNewAttr, aError);
}

already_AddRefed<nsIHTMLCollection> Element::GetElementsByTagNameNS(
    const nsAString& aNamespaceURI, const nsAString& aLocalName,
    ErrorResult& aError) {
  int32_t nameSpaceId = kNameSpaceID_Wildcard;

  if (!aNamespaceURI.EqualsLiteral("*")) {
    aError = nsNameSpaceManager::GetInstance()->RegisterNameSpace(aNamespaceURI,
                                                                  nameSpaceId);
    if (aError.Failed()) {
      return nullptr;
    }
  }

  NS_ASSERTION(nameSpaceId != kNameSpaceID_Unknown, "Unexpected namespace ID!");

  return NS_GetContentList(this, nameSpaceId, aLocalName);
}

bool Element::HasAttributeNS(const nsAString& aNamespaceURI,
                             const nsAString& aLocalName) const {
  int32_t nsid = nsNameSpaceManager::GetInstance()->GetNameSpaceID(
      aNamespaceURI, nsContentUtils::IsChromeDoc(OwnerDoc()));

  if (nsid == kNameSpaceID_Unknown) {
    // Unknown namespace means no attr...
    return false;
  }

  RefPtr<nsAtom> name = NS_AtomizeMainThread(aLocalName);
  return HasAttr(nsid, name);
}

already_AddRefed<nsIHTMLCollection> Element::GetElementsByClassName(
    const nsAString& aClassNames) {
  return nsContentUtils::GetElementsByClassName(this, aClassNames);
}

bool Element::HasSharedRoot(const Element* aElement) const {
  nsINode* root = SubtreeRoot();
  nsINode* attrSubtreeRoot = aElement->SubtreeRoot();
  do {
    if (root == attrSubtreeRoot) {
      return true;
    }
    auto* shadow = ShadowRoot::FromNode(root);
    if (!shadow || !shadow->GetHost()) {
      break;
    }
    root = shadow->GetHost()->SubtreeRoot();
  } while (true);
  return false;
}

Element* Element::GetElementByIdInDocOrSubtree(nsAtom* aID) const {
  if (auto* docOrShadowRoot = GetContainingDocumentOrShadowRoot()) {
    return docOrShadowRoot->GetElementById(aID);
  }

  return nsContentUtils::MatchElementId(SubtreeRoot()->AsContent(), aID);
}

Element* Element::GetAttrAssociatedElement(nsAtom* aAttr) const {
  if (const nsExtendedDOMSlots* slots = GetExistingExtendedDOMSlots()) {
    nsWeakPtr weakAttrEl = slots->mExplicitlySetAttrElementMap.Get(aAttr);
    if (nsCOMPtr<Element> attrEl = do_QueryReferent(weakAttrEl)) {
      // If reflectedTarget's explicitly set attr-element |attrEl| is
      // a descendant of any of element's shadow-including ancestors, then
      // return |atrEl|.
      if (HasSharedRoot(attrEl)) {
        return attrEl;
      }
      return nullptr;
    }
  }

  const nsAttrValue* value = GetParsedAttr(aAttr);
  if (!value) {
    return nullptr;
  }

  MOZ_ASSERT(value->Type() == nsAttrValue::eAtom,
             "Attribute used for attr associated element must be parsed");

  return GetElementByIdInDocOrSubtree(value->GetAtomValue());
}

void Element::GetAttrAssociatedElements(
    nsAtom* aAttr, bool* aUseCachedValue,
    Nullable<nsTArray<RefPtr<Element>>>& aElements) {
  MOZ_ASSERT(aElements.IsNull());

  auto& [explicitlySetAttrElements, cachedAttrElements] =
      ExtendedDOMSlots()->mAttrElementsMap.LookupOrInsert(aAttr);

  // https://html.spec.whatwg.org/multipage/common-dom-interfaces.html#attr-associated-elements
  auto getAttrAssociatedElements =
      [&, &explicitlySetAttrElements =
              explicitlySetAttrElements]() -> Maybe<nsTArray<RefPtr<Element>>> {
    nsTArray<RefPtr<Element>> elements;

    if (explicitlySetAttrElements) {
      // 3. If reflectedTarget's explicitly set attr-elements is not null
      for (const nsWeakPtr& weakEl : *explicitlySetAttrElements) {
        // For each attrElement in reflectedTarget's explicitly set
        // attr-elements:
        if (nsCOMPtr<Element> attrEl = do_QueryReferent(weakEl)) {
          // If attrElement is not a descendant of any of element's
          // shadow-including ancestors, then continue.
          if (!HasSharedRoot(attrEl)) {
            continue;
          }
          // Append attrElement to elements.
          elements.AppendElement(attrEl);
        }
      }
    } else {
      // 4. Otherwise
      //   1. Let contentAttributeValue be the result of running
      //   reflectedTarget's get the content attribute.
      const nsAttrValue* value = GetParsedAttr(aAttr);
      //   2. If contentAttributeValue is null, then return null.
      if (!value) {
        return Nothing();
      }

      //   3. Let tokens be contentAttributeValue, split on ASCII whitespace.
      MOZ_ASSERT(value->Type() == nsAttrValue::eAtomArray ||
                     value->Type() == nsAttrValue::eAtom,
                 "Attribute used for attr associated elements must be parsed");
      for (uint32_t i = 0; i < value->GetAtomCount(); i++) {
        // For each id of tokens:
        if (auto* candidate = GetElementByIdInDocOrSubtree(
                value->AtomAt(static_cast<int32_t>(i)))) {
          // Append candidate to elements.
          elements.AppendElement(candidate);
        }
      }
    }

    return Some(std::move(elements));
  };

  // getter steps:
  // 1. Let elements be the result of running this's get the attr-associated
  // elements.
  auto elements = getAttrAssociatedElements();

  if (elements && elements == cachedAttrElements) {
    // 2. If the contents of elements is equal to the contents of this's cached
    // attr-associated elements, then return this's cached attr-associated
    // elements object.
    MOZ_ASSERT(!*aUseCachedValue);
    *aUseCachedValue = true;
    return;
  }

  // 3. Let elementsAsFrozenArray be elements, converted to a FrozenArray<T>?.
  //    (the binding code takes aElements and returns it as a FrozenArray)
  // 5. Set this's cached attr-associated elements object to
  //    elementsAsFrozenArray.
  //    (the binding code stores the attr-associated elements object in a slot)
  // 6. Return elementsAsFrozenArray.
  if (elements) {
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