Accessible*
nsAccessiblePivot::AdjustStartPosition(Accessible* aAccessible,
RuleCache& aCache,
uint16_t* aFilterResult,
nsresult* aResult)
{
Accessible* matched = aAccessible;
*aResult = aCache.ApplyFilter(aAccessible, aFilterResult);
if (aAccessible != mRoot && aAccessible != mModalRoot) {
for (Accessible* temp = aAccessible->Parent();
temp && temp != mRoot && temp != mModalRoot; temp = temp->Parent()) {
uint16_t filtered = nsIAccessibleTraversalRule::FILTER_IGNORE;
*aResult = aCache.ApplyFilter(temp, &filtered);
NS_ENSURE_SUCCESS(*aResult, nullptr);
if (filtered & nsIAccessibleTraversalRule::FILTER_IGNORE_SUBTREE) {
*aFilterResult = filtered;
matched = temp;
}
}
}
if (aAccessible == mPosition && mStartOffset != -1 && mEndOffset != -1) {
HyperTextAccessible* text = aAccessible->AsHyperText();
if (text) {
matched = text->GetChildAtOffset(mStartOffset);
}
}
return matched;
}
static gchar*
getTextAtOffsetCB(AtkText *aText, gint aOffset,
AtkTextBoundary aBoundaryType,
gint *aStartOffset, gint *aEndOffset)
{
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
if (!accWrap)
return nullptr;
HyperTextAccessible* text = accWrap->AsHyperText();
if (!text || !text->IsTextRole())
return nullptr;
nsAutoString autoStr;
int32_t startOffset = 0, endOffset = 0;
nsresult rv =
text->GetTextAtOffset(aOffset, aBoundaryType,
&startOffset, &endOffset, autoStr);
*aStartOffset = startOffset;
*aEndOffset = endOffset;
NS_ENSURE_SUCCESS(rv, nullptr);
ConvertTexttoAsterisks(accWrap, autoStr);
NS_ConvertUTF16toUTF8 cautoStr(autoStr);
return (cautoStr.get()) ? g_strdup(cautoStr.get()) : nullptr;
}
void
EventQueue::CreateTextChangeEventFor(AccMutationEvent* aEvent)
{
Accessible* container = aEvent->mAccessible->Parent();
if (!container)
return;
HyperTextAccessible* textAccessible = container->AsHyperText();
if (!textAccessible)
return;
// Don't fire event for the first html:br in an editor.
if (aEvent->mAccessible->Role() == roles::WHITESPACE) {
nsCOMPtr<nsIEditor> editor = textAccessible->GetEditor();
if (editor) {
bool isEmpty = false;
editor->GetDocumentIsEmpty(&isEmpty);
if (isEmpty)
return;
}
}
int32_t offset = textAccessible->GetChildOffset(aEvent->mAccessible);
nsAutoString text;
aEvent->mAccessible->AppendTextTo(text);
if (text.IsEmpty())
return;
aEvent->mTextChangeEvent =
new AccTextChangeEvent(textAccessible, offset, text, aEvent->IsShow(),
aEvent->mIsFromUserInput ? eFromUserInput : eNoUserInput);
}
static void
getRangeExtentsCB(AtkText *aText, gint aStartOffset, gint aEndOffset,
AtkCoordType aCoords, AtkTextRectangle *aRect)
{
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
if(!accWrap || !aRect)
return;
HyperTextAccessible* text = accWrap->AsHyperText();
if (!text || !text->IsTextRole())
return;
int32_t extY = 0, extX = 0;
int32_t extWidth = 0, extHeight = 0;
uint32_t geckoCoordType;
if (aCoords == ATK_XY_SCREEN)
geckoCoordType = nsIAccessibleCoordinateType::COORDTYPE_SCREEN_RELATIVE;
else
geckoCoordType = nsIAccessibleCoordinateType::COORDTYPE_WINDOW_RELATIVE;
#ifdef DEBUG
nsresult rv =
#endif
text->GetRangeExtents(aStartOffset, aEndOffset,
&extX, &extY,
&extWidth, &extHeight,
geckoCoordType);
aRect->x = extX;
aRect->y = extY;
aRect->width = extWidth;
aRect->height = extHeight;
NS_ASSERTION(NS_SUCCEEDED(rv),
"MaiInterfaceText::GetRangeExtents, failed\n");
}
static gchar*
getTextSelectionCB(AtkText *aText, gint aSelectionNum,
gint *aStartOffset, gint *aEndOffset)
{
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
int32_t startOffset = 0, endOffset = 0;
if (accWrap) {
HyperTextAccessible* text = accWrap->AsHyperText();
if (!text || !text->IsTextRole()) {
return nullptr;
}
text->SelectionBoundsAt(aSelectionNum, &startOffset, &endOffset);
*aStartOffset = startOffset;
*aEndOffset = endOffset;
return getTextCB(aText, *aStartOffset, *aEndOffset);
} else if (ProxyAccessible* proxy = GetProxy(ATK_OBJECT(aText))) {
nsString data;
proxy->SelectionBoundsAt(aSelectionNum, data, &startOffset, &endOffset);
*aStartOffset = startOffset;
*aEndOffset = endOffset;
NS_ConvertUTF16toUTF8 dataAsUTF8(data);
return (dataAsUTF8.get()) ? g_strdup(dataAsUTF8.get()) : nullptr;
}
return nullptr;
}
static AtkAttributeSet*
getRunAttributesCB(AtkText *aText, gint aOffset,
gint *aStartOffset,
gint *aEndOffset)
{
*aStartOffset = -1;
*aEndOffset = -1;
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
if (!accWrap)
return nullptr;
HyperTextAccessible* text = accWrap->AsHyperText();
if (!text || !text->IsTextRole())
return nullptr;
nsCOMPtr<nsIPersistentProperties> attributes;
int32_t startOffset = 0, endOffset = 0;
nsresult rv = text->GetTextAttributes(false, aOffset,
&startOffset, &endOffset,
getter_AddRefs(attributes));
NS_ENSURE_SUCCESS(rv, nullptr);
*aStartOffset = startOffset;
*aEndOffset = endOffset;
return ConvertToAtkAttributeSet(attributes);
}
static void
getRangeExtentsCB(AtkText *aText, gint aStartOffset, gint aEndOffset,
AtkCoordType aCoords, AtkTextRectangle *aRect)
{
if (!aRect) {
return;
}
nsIntRect rect;
uint32_t geckoCoordType;
if (aCoords == ATK_XY_SCREEN) {
geckoCoordType = nsIAccessibleCoordinateType::COORDTYPE_SCREEN_RELATIVE;
} else {
geckoCoordType = nsIAccessibleCoordinateType::COORDTYPE_WINDOW_RELATIVE;
}
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
if(accWrap) {
HyperTextAccessible* text = accWrap->AsHyperText();
if (!text || !text->IsTextRole()) {
return;
}
rect = text->TextBounds(aStartOffset, aEndOffset, geckoCoordType);
} else if (ProxyAccessible* proxy = GetProxy(ATK_OBJECT(aText))) {
rect = proxy->TextBounds(aStartOffset, aEndOffset, geckoCoordType);
} else {
return;
}
aRect->x = rect.x;
aRect->y = rect.y;
aRect->width = rect.width;
aRect->height = rect.height;
}
static gint
getOffsetAtPointCB(AtkText *aText,
gint aX, gint aY,
AtkCoordType aCoords)
{
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
if (accWrap) {
HyperTextAccessible* text = accWrap->AsHyperText();
if (!text || !text->IsTextRole()) {
return -1;
}
return static_cast<gint>(
text->OffsetAtPoint(aX, aY,
(aCoords == ATK_XY_SCREEN ?
nsIAccessibleCoordinateType::COORDTYPE_SCREEN_RELATIVE :
nsIAccessibleCoordinateType::COORDTYPE_WINDOW_RELATIVE)));
}
if (ProxyAccessible* proxy = GetProxy(ATK_OBJECT(aText))) {
return static_cast<gint>(
proxy->OffsetAtPoint(aX, aY,
(aCoords == ATK_XY_SCREEN ?
nsIAccessibleCoordinateType::COORDTYPE_SCREEN_RELATIVE :
nsIAccessibleCoordinateType::COORDTYPE_WINDOW_RELATIVE)));
}
return -1;
}
static gchar*
getTextBeforeOffsetCB(AtkText *aText, gint aOffset,
AtkTextBoundary aBoundaryType,
gint *aStartOffset, gint *aEndOffset)
{
nsAutoString autoStr;
int32_t startOffset = 0, endOffset = 0;
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
if (accWrap) {
HyperTextAccessible* text = accWrap->AsHyperText();
if (!text || !text->IsTextRole())
return nullptr;
text->TextBeforeOffset(aOffset, aBoundaryType,
&startOffset, &endOffset, autoStr);
ConvertTexttoAsterisks(accWrap, autoStr);
} else if (ProxyAccessible* proxy = GetProxy(ATK_OBJECT(aText))) {
proxy->GetTextBeforeOffset(aOffset, aBoundaryType, autoStr, &startOffset,
&endOffset);
}
*aStartOffset = startOffset;
*aEndOffset = endOffset;
NS_ConvertUTF16toUTF8 cautoStr(autoStr);
return (cautoStr.get()) ? g_strdup(cautoStr.get()) : nullptr;
}
void
SelectionManager::NormalSelectionChanged(nsISelection* aSelection)
{
mLastUsedSelection = do_GetWeakReference(aSelection);
int32_t rangeCount = 0;
aSelection->GetRangeCount(&rangeCount);
if (rangeCount == 0) {
mLastTextAccessible = nullptr;
return; // No selection
}
HyperTextAccessible* textAcc =
nsAccUtils::GetTextAccessibleFromSelection(aSelection);
if (!textAcc)
return;
int32_t caretOffset = -1;
nsresult rv = textAcc->GetCaretOffset(&caretOffset);
if (NS_FAILED(rv))
return;
if (textAcc == mLastTextAccessible && caretOffset == mLastCaretOffset) {
int32_t selectionCount = 0;
textAcc->GetSelectionCount(&selectionCount); // Don't swallow similar events when selecting text
if (!selectionCount)
return; // Swallow duplicate caret event
}
mLastCaretOffset = caretOffset;
mLastTextAccessible = textAcc;
nsRefPtr<AccEvent> event = new AccCaretMoveEvent(mLastTextAccessible);
mLastTextAccessible->Document()->FireDelayedEvent(event);
}
void
SelectionManager::ProcessSelectionChanged(nsISelection* aSelection)
{
Selection* selection = static_cast<Selection*>(aSelection);
const nsRange* range = selection->GetAnchorFocusRange();
nsINode* cntrNode = nullptr;
if (range)
cntrNode = range->GetCommonAncestor();
if (!cntrNode) {
cntrNode = selection->GetFrameSelection()->GetAncestorLimiter();
if (!cntrNode) {
cntrNode = selection->GetPresShell()->GetDocument();
NS_ASSERTION(selection->GetPresShell()->ConstFrameSelection() == selection->GetFrameSelection(),
"Wrong selection container was used!");
}
}
HyperTextAccessible* text = nsAccUtils::GetTextContainer(cntrNode);
if (!text) {
NS_NOTREACHED("We must reach document accessible implementing text interface!");
return;
}
if (selection->GetType() == nsISelectionController::SELECTION_NORMAL) {
nsRefPtr<AccEvent> event = new AccTextSelChangeEvent(text, aSelection);
text->Document()->FireDelayedEvent(event);
} else if (selection->GetType() == nsISelectionController::SELECTION_SPELLCHECK) {
// XXX: fire an event for container accessible of the focus/anchor range
// of the spelcheck selection.
text->Document()->FireDelayedEvent(nsIAccessibleEvent::EVENT_TEXT_ATTRIBUTE_CHANGED,
text);
}
}
void
SelectionManager::ProcessTextSelChangeEvent(AccEvent* aEvent)
{
AccTextSelChangeEvent* event = downcast_accEvent(aEvent);
Selection* sel = static_cast<Selection*>(event->mSel.get());
// Fire selection change event if it's not pure caret-move selection change.
if (sel->GetRangeCount() != 1 || !sel->IsCollapsed())
nsEventShell::FireEvent(aEvent);
// Fire caret move event if there's a caret in the selection.
nsINode* caretCntrNode =
nsCoreUtils::GetDOMNodeFromDOMPoint(sel->GetFocusNode(),
sel->GetFocusOffset());
if (!caretCntrNode)
return;
HyperTextAccessible* caretCntr = nsAccUtils::GetTextContainer(caretCntrNode);
NS_ASSERTION(caretCntr,
"No text container for focus while there's one for common ancestor?!");
if (!caretCntr)
return;
int32_t caretOffset = -1;
if (NS_SUCCEEDED(caretCntr->GetCaretOffset(&caretOffset)) && caretOffset != -1) {
nsRefPtr<AccCaretMoveEvent> caretMoveEvent =
new AccCaretMoveEvent(caretCntr, caretOffset, aEvent->FromUserInput());
nsEventShell::FireEvent(caretMoveEvent);
}
}
void SelectionManager::ProcessTextSelChangeEvent(AccEvent* aEvent) {
// Fire selection change event if it's not pure caret-move selection change,
// i.e. the accessible has or had not collapsed selection.
AccTextSelChangeEvent* event = downcast_accEvent(aEvent);
if (!event->IsCaretMoveOnly()) nsEventShell::FireEvent(aEvent);
// Fire caret move event if there's a caret in the selection.
nsINode* caretCntrNode = nsCoreUtils::GetDOMNodeFromDOMPoint(
event->mSel->GetFocusNode(), event->mSel->FocusOffset());
if (!caretCntrNode) return;
HyperTextAccessible* caretCntr = nsAccUtils::GetTextContainer(caretCntrNode);
NS_ASSERTION(
caretCntr,
"No text container for focus while there's one for common ancestor?!");
if (!caretCntr) return;
Selection* selection = caretCntr->DOMSelection();
// XXX Sometimes we can't get a selection for caretCntr, in that case assume
// event->mSel is correct.
if (!selection) selection = event->mSel;
mCaretOffset = caretCntr->DOMPointToOffset(selection->GetFocusNode(),
selection->FocusOffset());
mAccWithCaret = caretCntr;
if (mCaretOffset != -1) {
RefPtr<AccCaretMoveEvent> caretMoveEvent =
new AccCaretMoveEvent(caretCntr, mCaretOffset, aEvent->FromUserInput());
nsEventShell::FireEvent(caretMoveEvent);
}
}
/* private */
PRUint16
AccessibleWrap::CreateMaiInterfaces(void)
{
PRUint16 interfacesBits = 0;
// The Component interface is supported by all accessibles.
interfacesBits |= 1 << MAI_INTERFACE_COMPONENT;
// Add Action interface if the action count is more than zero.
if (ActionCount() > 0)
interfacesBits |= 1 << MAI_INTERFACE_ACTION;
// Text, Editabletext, and Hypertext interface.
HyperTextAccessible* hyperText = AsHyperText();
if (hyperText && hyperText->IsTextRole()) {
interfacesBits |= 1 << MAI_INTERFACE_TEXT;
interfacesBits |= 1 << MAI_INTERFACE_EDITABLE_TEXT;
if (!nsAccUtils::MustPrune(this))
interfacesBits |= 1 << MAI_INTERFACE_HYPERTEXT;
}
// Value interface.
nsCOMPtr<nsIAccessibleValue> accessInterfaceValue;
QueryInterface(NS_GET_IID(nsIAccessibleValue),
getter_AddRefs(accessInterfaceValue));
if (accessInterfaceValue) {
interfacesBits |= 1 << MAI_INTERFACE_VALUE;
}
// Document interface.
if (IsDoc())
interfacesBits |= 1 << MAI_INTERFACE_DOCUMENT;
if (IsImage())
interfacesBits |= 1 << MAI_INTERFACE_IMAGE;
// HyperLink interface.
if (IsLink())
interfacesBits |= 1 << MAI_INTERFACE_HYPERLINK_IMPL;
if (!nsAccUtils::MustPrune(this)) { // These interfaces require children
// Table interface.
nsCOMPtr<nsIAccessibleTable> accessInterfaceTable;
QueryInterface(NS_GET_IID(nsIAccessibleTable),
getter_AddRefs(accessInterfaceTable));
if (accessInterfaceTable) {
interfacesBits |= 1 << MAI_INTERFACE_TABLE;
}
// Selection interface.
if (IsSelect()) {
interfacesBits |= 1 << MAI_INTERFACE_SELECTION;
}
}
return interfacesBits;
}
NS_IMETHODIMP
xpcAccessibleHyperText::AddSelection(int32_t aStartOffset, int32_t aEndOffset)
{
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->AddToSelection(aStartOffset, aEndOffset);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::SetTextContents(const nsAString& aText)
{
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->ReplaceText(aText);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::ScriptablePasteText(int32_t aOffset)
{
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->PasteText(aOffset);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::RemoveSelection(int32_t aSelectionNum)
{
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->RemoveFromSelection(aSelectionNum);
return NS_OK;
}
NS_IMETHODIMP
nsAccessiblePivot::MovePreviousByText(TextBoundaryType aBoundary, bool* aResult)
{
NS_ENSURE_ARG(aResult);
*aResult = false;
int32_t oldStart = mStartOffset, oldEnd = mEndOffset;
HyperTextAccessible* text = mPosition->AsHyperText();
Accessible* oldPosition = mPosition;
while (!text) {
oldPosition = mPosition;
mPosition = mPosition->Parent();
text = mPosition->AsHyperText();
}
if (mStartOffset == -1)
mStartOffset = text != oldPosition ? text->GetChildOffset(oldPosition) : 0;
if (mStartOffset == 0)
return NS_OK;
AccessibleTextBoundary startBoundary, endBoundary;
switch (aBoundary) {
case CHAR_BOUNDARY:
startBoundary = nsIAccessibleText::BOUNDARY_CHAR;
endBoundary = nsIAccessibleText::BOUNDARY_CHAR;
break;
case WORD_BOUNDARY:
startBoundary = nsIAccessibleText::BOUNDARY_WORD_START;
endBoundary = nsIAccessibleText::BOUNDARY_WORD_END;
break;
default:
return NS_ERROR_INVALID_ARG;
}
nsAutoString unusedText;
int32_t newStart = 0, newEnd = 0;
text->GetTextBeforeOffset(mStartOffset, startBoundary, &newStart, &newEnd,
unusedText);
if (newStart < mStartOffset)
mStartOffset = newEnd == mStartOffset ? newStart : newEnd;
else // XXX: In certain odd cases newStart is equal to mStartOffset
text->GetTextBeforeOffset(mStartOffset - 1, startBoundary, &newStart,
&mStartOffset, unusedText);
text->GetTextAtOffset(mStartOffset, endBoundary, &newStart, &mEndOffset,
unusedText);
*aResult = true;
NotifyOfPivotChange(mPosition, oldStart, oldEnd,
nsIAccessiblePivot::REASON_TEXT);
return NS_OK;
}
static gint
getCharacterCountCB(AtkText *aText)
{
AccessibleWrap* accWrap = GetAccessibleWrap(ATK_OBJECT(aText));
if (!accWrap)
return 0;
HyperTextAccessible* textAcc = accWrap->AsHyperText();
return textAcc->IsDefunct() ?
0 : static_cast<gint>(textAcc->CharacterCount());
}
NS_IMETHODIMP
xpcAccessibleHyperText::ScriptableCutText(int32_t aStartOffset,
int32_t aEndOffset)
{
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->CutText(aStartOffset, aEndOffset);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::ScriptableInsertText(const nsAString& aText,
int32_t aOffset)
{
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->InsertText(aText, aOffset);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::ScriptableScrollSubstringTo(int32_t aStartOffset,
int32_t aEndOffset,
uint32_t aScrollType)
{
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->ScrollSubstringTo(aStartOffset, aEndOffset, aScrollType);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::GetText(int32_t aStartOffset, int32_t aEndOffset,
nsAString& aText)
{
aText.Truncate();
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
text->TextSubstring(aStartOffset, aEndOffset, aText);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::GetLinkCount(int32_t* aLinkCount)
{
NS_ENSURE_ARG_POINTER(aLinkCount);
*aLinkCount = 0;
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
*aLinkCount = text->LinkCount();
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::GetScriptableCaretOffset(int32_t* aCaretOffset)
{
NS_ENSURE_ARG_POINTER(aCaretOffset);
*aCaretOffset = -1;
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
*aCaretOffset = text->CaretOffset();
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::GetDefaultTextAttributes(nsIPersistentProperties** aAttributes)
{
NS_ENSURE_ARG_POINTER(aAttributes);
*aAttributes = nullptr;
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
nsCOMPtr<nsIPersistentProperties> attrs = text->DefaultTextAttributes();
attrs.swap(*aAttributes);
return NS_OK;
}
NS_IMETHODIMP
xpcAccessibleHyperText::GetOffsetAtPoint(int32_t aX, int32_t aY,
uint32_t aCoordType, int32_t* aOffset)
{
NS_ENSURE_ARG_POINTER(aOffset);
*aOffset = -1;
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
*aOffset = text->OffsetAtPoint(aX, aY, aCoordType);
return NS_OK;
}
STDMETHODIMP
ia2AccessibleText::addSelection(long aStartOffset, long aEndOffset)
{
A11Y_TRYBLOCK_BEGIN
HyperTextAccessible* textAcc = static_cast<HyperTextAccessibleWrap*>(this);
if (textAcc->IsDefunct())
return CO_E_OBJNOTCONNECTED;
return textAcc->AddToSelection(aStartOffset, aEndOffset) ?
S_OK : E_INVALIDARG;
A11Y_TRYBLOCK_END
}
NS_IMETHODIMP
xpcAccessibleHyperText::GetLinkIndexAtOffset(int32_t aOffset,
int32_t* aLinkIndex)
{
NS_ENSURE_ARG_POINTER(aLinkIndex);
*aLinkIndex = -1; // API says this magic value means 'not found'
HyperTextAccessible* text = static_cast<HyperTextAccessible*>(this);
if (text->IsDefunct())
return NS_ERROR_FAILURE;
*aLinkIndex = text->LinkIndexAtOffset(aOffset);
return NS_OK;
}