def shouldAcceptEvent(eventName, windowHandle=None):
	"""Check whether an event should be accepted from a platform API.
	Creating NVDAObjects and executing events can be expensive
	and might block the main thread noticeably if the object is slow to respond.
	Therefore, this should be used before NVDAObject creation to filter out any unnecessary events.
	A platform API handler may do its own filtering before this.
	"""
	if not windowHandle:
		# We can't filter without a window handle.
		return True
	key = (eventName,
		winUser.getWindowThreadProcessID(windowHandle)[0],
		winUser.getClassName(windowHandle))
	if key in _acceptEvents:
		return True
	if eventName == "valueChange" and config.conf["presentation"]["progressBarUpdates"]["reportBackgroundProgressBars"]:
		return True
	if eventName == "show":
		# Only accept 'show' events for specific cases, as otherwise we get flooded.
		return winUser.getClassName(windowHandle) in (
			"Frame Notification Bar", # notification bars
			"tooltips_class32", # tooltips
			"mscandui21.candidate", "mscandui40.candidate", "MSCandUIWindow_Candidate", # IMM candidates
			"TTrayAlert", # 5405: Skype
		)
	if eventName == "reorder":
		# Prevent another flood risk.
		return winUser.getClassName(windowHandle) == "TTrayAlert" # #4841: Skype
	if eventName == "alert" and winUser.getClassName(winUser.getAncestor(windowHandle, winUser.GA_PARENT)) == "ToastChildWindowClass":
		# Toast notifications.
		return True
	if eventName in ("menuEnd", "switchEnd", "desktopSwitch"):
		# #5302, #5462: These events can be fired on the desktop window
		# or windows that would otherwise be blocked.
		# Platform API handlers will translate these events to focus events anyway,
		# so we must allow them here.
		return True
	if windowHandle == winUser.getDesktopWindow():
		# #5595: Events for the cursor get mapped to the desktop window.
		return True

	fg = winUser.getForegroundWindow()
	if (winUser.isDescendantWindow(fg, windowHandle)
			# #3899, #3905: Covers cases such as the Firefox Page Bookmarked window and OpenOffice/LibreOffice context menus.
			or winUser.isDescendantWindow(fg, winUser.getAncestor(windowHandle, winUser.GA_ROOTOWNER))):
		# This is for the foreground application.
		return True
	if (winUser.user32.GetWindowLongW(windowHandle, winUser.GWL_EXSTYLE) & winUser.WS_EX_TOPMOST
			or winUser.user32.GetWindowLongW(winUser.getAncestor(windowHandle, winUser.GA_ROOT), winUser.GWL_EXSTYLE) & winUser.WS_EX_TOPMOST):
		# This window or its root is a topmost window.
		# This includes menus, combo box pop-ups and the task switching list.
		return True
	return False

	def __contains__(self,obj):
		if not obj.windowClassName.startswith("Internet Explorer_"):
			return False
		#'select' tag lists have MSAA list items which do not relate to real HTML nodes.
		#Go up one parent for these and use it instead
		if isinstance(obj,NVDAObjects.IAccessible.IAccessible) and not isinstance(obj,NVDAObjects.IAccessible.MSHTML.MSHTML) and obj.role==controlTypes.ROLE_LISTITEM:
			parent=obj.parent
			if parent and isinstance(parent,NVDAObjects.IAccessible.MSHTML.MSHTML):
				obj=parent
		#Combo box lists etc are popup windows, so rely on accessibility hierarchi instead of window hierarchi for those.
		#However only helps in IE8.
		if obj.windowStyle&winUser.WS_POPUP:
			parent=obj.parent
			obj.parent=parent
			while parent and parent.windowHandle==obj.windowHandle:
				newParent=parent.parent
				parent.parent=newParent
				parent=newParent
			if parent and parent.windowClassName.startswith('Internet Explorer_'):
				obj=parent
		if not winUser.isDescendantWindow(self.rootDocHandle,obj.windowHandle) and obj.windowHandle!=self.rootDocHandle:
			return False
		newObj=obj
		while  isinstance(newObj,NVDAObjects.IAccessible.MSHTML.MSHTML):
			if newObj==self.rootNVDAObject:
				return True
			if newObj.role in (controlTypes.ROLE_APPLICATION,controlTypes.ROLE_DIALOG):
				break
			newObj=newObj.parent 
		return False

def event_gainFocus(vmID,accContext):
	tempContext=accContext
	while tempContext:
		try:
			tempContext=bridgeDll.getActiveDescendent(vmID,tempContext)
		except:
			tempContext=None
		try:
			depth=bridgeDll.getObjectDepth(vmID,tempContext)
		except:
			depth=-1
		if tempContext and (depth<=0 or bridgeDll.isSameObject(vmID,accContext,tempContext)):
			tempContext=None
		if tempContext:
			bridgeDll.releaseJavaObject(vmID,accContext)
			accContext=tempContext
	jabContext=JABContext(vmID=vmID,accContext=accContext)
	if not winUser.isDescendantWindow(winUser.getForegroundWindow(),jabContext.hwnd):
		return
	focus=eventHandler.lastQueuedFocusObject
	if (isinstance(focus,NVDAObjects.JAB.JAB) and focus.jabContext==jabContext):
		return 
	obj=NVDAObjects.JAB.JAB(jabContext=jabContext)
	if obj.role==controlTypes.ROLE_UNKNOWN:
		return
	eventHandler.queueEvent("gainFocus",obj)

	def event_gainFocus(self, obj, nextHandler):
		if self.chatWindow and not winUser.isDescendantWindow(self.chatWindow, obj.windowHandle):
			self.conversationLostFocus()
		# A conversation might have its own top level window,
		# but foreground changes often trigger gainFocus instead of focusEntered.
		self.conversationMaybeFocused(obj)
		nextHandler()

	def event_valueChange(self):
		global lastMSNHistoryValue
		if winUser.isDescendantWindow(winUser.getForegroundWindow(),self.windowHandle):
			value=self.value
			if value!=lastMSNHistoryValue and config.conf["presentation"]["reportDynamicContentChanges"]:
				speech.speakText(value)
				lastMSNHistoryValue=value

	def event_valueChange(self):
		if self.event_childID==0 and self.event_objectID == winUser.OBJID_CLIENT and winUser.isDescendantWindow(winUser.getForegroundWindow(),self.windowHandle):
			# Acrobat has indicated that a page has died and been replaced by a new one.
			# The new page has the same event params, so we must bypass NVDA's IAccessible caching.
			obj = getNVDAObjectFromEvent(self.windowHandle, -4, 0)
			if not obj:
				return
			eventHandler.queueEvent("gainFocus",obj)

	def _getNVDAObjectFromOffset(self,offset):
		try:
			p=self._getPointFromOffset(offset)
		except (NotImplementedError,LookupError):
			return self.obj
		obj=api.getDesktopObject().objectFromPoint(p.x,p.y)
		from NVDAObjects.window import Window
		if not obj or not isinstance(obj,Window) or not winUser.isDescendantWindow(self.obj.windowHandle,obj.windowHandle):
			return self.obj
		return obj

def event_gainFocus(vmID,accContext,hwnd):
	jabContext=JABContext(hwnd=hwnd,vmID=vmID,accContext=accContext)
	if not winUser.isDescendantWindow(winUser.getForegroundWindow(),jabContext.hwnd):
		return
	focus=eventHandler.lastQueuedFocusObject
	if (isinstance(focus,NVDAObjects.JAB.JAB) and focus.jabContext==jabContext):
		return 
	obj=NVDAObjects.JAB.JAB(jabContext=jabContext)
	if obj.role==controlTypes.ROLE_UNKNOWN:
		return
	eventHandler.queueEvent("gainFocus",obj)

	def _get_SDMChild(self):
		if controlTypes.STATE_FOCUSED in self.states:
			hwndFocus=winUser.getGUIThreadInfo(0).hwndFocus
			if hwndFocus and hwndFocus!=self.windowHandle and winUser.isDescendantWindow(self.windowHandle,hwndFocus) and not winUser.getClassName(hwndFocus).startswith('bosa_sdm'):
				obj=getNVDAObjectFromEvent(hwndFocus,winUser.OBJID_CLIENT,0)
				if not obj: return None
				if getattr(obj,'parentSDMCanOverrideName',True):
					obj.name=self.name
				obj.keyboardShortcut=self.keyboardShortcut
				obj.parent=self
				return obj
		return None

	def event_stateChange(self):
		# iTunes has indicated that a page has died and been replaced by a new one.
		focus = api.getFocusObject()
		if not winUser.isDescendantWindow(self.windowHandle, focus.windowHandle):
			return
		if focus.role:
			# The old document is still alive.
			return
		# The new page has the same event params, so we must bypass NVDA's IAccessible caching.
		obj = NVDAObjects.IAccessible.getNVDAObjectFromEvent(focus.windowHandle, winUser.OBJID_CLIENT, 0)
		if not obj:
			return
		eventHandler.queueEvent("gainFocus",obj)

	def event_stateChange(self):
		# iTunes has indicated that a page has died and been replaced by a new one.
		focus = api.getFocusObject()
		if not winUser.isDescendantWindow(self.windowHandle, focus.windowHandle):
			return
		# The new page has the same event params, so we must bypass NVDA's IAccessible caching.
		obj = NVDAObjects.IAccessible.getNVDAObjectFromEvent(focus.windowHandle, winUser.OBJID_CLIENT, 0)
		if not obj:
			return
		if focus.treeInterceptor:
			speech.cancelSpeech()
			treeInterceptorHandler.killTreeInterceptor(focus.treeInterceptor)
		eventHandler.queueEvent("gainFocus",obj)

	def __contains__(self,obj):
		if self.isWindowless:
			if not isinstance(obj, NVDAObjects.IAccessible.IAccessible):
				return False
			if obj.windowHandle != self.rootDocHandle:
				return False
			info = obj.IAccessibleIdentity
			if not info:
				return False
			ID=info['objectID']
			try:
				self.rootNVDAObject.IAccessibleObject.accChild(ID)
				return True
			except COMError:
				return False
		return winUser.isDescendantWindow(self.rootDocHandle, obj.windowHandle)

def processFocusWinEvent(window,objectID,childID,force=False):
	"""checks to see if the focus win event is not the same as the existing focus, 
	then converts the win event to an NVDA event (instanciating an NVDA Object) then calls processFocusNVDAEvent. If all is ok it returns True.
	@type window: integer
	@param objectID: a win event's object ID
	@type objectID: integer
	@param childID: a win event's child ID
	@type childID: integer
	@param force: If True, the shouldAllowIAccessibleFocusEvent property of the object is ignored.
	@type force: boolean
	@returns: True if the focus is valid and was handled, False otherwise.
	@rtype: boolean
	"""
	windowClassName=winUser.getClassName(window)
	# Generally, we must ignore focus on child windows of SDM windows as we only want the SDM MSAA events.
	# However, we don't want to ignore focus if the child ID isn't 0,
	# as this is a child control and the SDM MSAA events don't handle child controls.
	if childID==0 and not windowClassName.startswith('bosa_sdm') and winUser.getClassName(winUser.getAncestor(window,winUser.GA_PARENT)).startswith('bosa_sdm'):
		return False
	rootWindow=winUser.getAncestor(window,winUser.GA_ROOT)
	# If this window is not within the foreground window and this window or its root window is not a popup window, and this window's root window is not the highest in the z-order
	if not winUser.isDescendantWindow(winUser.getForegroundWindow(),window) and not (winUser.getWindowStyle(window) & winUser.WS_POPUP or winUser.getWindowStyle(rootWindow)&winUser.WS_POPUP) and winUser.getPreviousWindow(rootWindow)!=0: 
		# This is a focus event from a background window, so ignore it.
		return False
	#Notify appModuleHandler of this new foreground window
	appModuleHandler.update(winUser.getWindowThreadProcessID(window)[0])
	#If Java access bridge is running, and this is a java window, then pass it to java and forget about it
	if JABHandler.isRunning and JABHandler.isJavaWindow(window):
		JABHandler.event_enterJavaWindow(window)
		return True
	#Convert the win event to an NVDA event
	NVDAEvent=winEventToNVDAEvent(winUser.EVENT_OBJECT_FOCUS,window,objectID,childID,useCache=False)
	if not NVDAEvent:
		return False
	eventName,obj=NVDAEvent
	if (childID==0 and obj.IAccessibleRole==oleacc.ROLE_SYSTEM_LIST) or (objectID==winUser.OBJID_CLIENT and "SysListView32" in obj.windowClassName):
		# Some controls incorrectly fire focus on child ID 0, even when there is a child with focus.
		try:
			realChildID=obj.IAccessibleObject.accFocus
		except:
			realChildID=None
		if isinstance(realChildID,int) and realChildID>0 and realChildID!=childID:
			realObj=NVDAObjects.IAccessible.IAccessible(IAccessibleObject=obj.IAccessibleObject,IAccessibleChildID=realChildID,event_windowHandle=window,event_objectID=objectID,event_childID=realChildID)
			if realObj:
				obj=realObj
	return processFocusNVDAEvent(obj,force=force)

def _shouldRecoverAfterMinTimeout():
	info=winUser.getGUIThreadInfo(0)
	#If hwndFocus is 0, then the OS is clearly busy and we don't want to timeout prematurely.
	if not info.hwndFocus: return False
	# Import late to avoid circular import.
	import api
	#If a system menu has been activated but NVDA's focus is not yet in the menu then use min timeout
	if info.flags&winUser.GUI_SYSTEMMENUMODE and info.hwndMenuOwner and api.getFocusObject().windowClassName!='#32768':
		return True 
	if winUser.getClassName(info.hwndFocus) in safeWindowClassSet:
		return False
	if not winUser.isDescendantWindow(info.hwndActive, api.getFocusObject().windowHandle):
		# The foreground window has changed.
		return True
	newHwnd=info.hwndFocus
	newThreadID=winUser.getWindowThreadProcessID(newHwnd)[1]
	return newThreadID!=api.getFocusObject().windowThreadID

def _shouldRecoverAfterMinTimeout():
	info=winUser.getGUIThreadInfo(0)
	if not info.hwndFocus:
		# The foreground thread is frozen or there is no foreground thread (probably due to a freeze elsewhere).
		return True
	# Import late to avoid circular import.
	import api
	#If a system menu has been activated but NVDA's focus is not yet in the menu then use min timeout
	if info.flags&winUser.GUI_SYSTEMMENUMODE and info.hwndMenuOwner and api.getFocusObject().windowClassName!='#32768':
		return True 
	if winUser.getClassName(info.hwndFocus) in safeWindowClassSet:
		return False
	if not winUser.isDescendantWindow(info.hwndActive, api.getFocusObject().windowHandle):
		# The foreground window has changed.
		return True
	newHwnd=info.hwndFocus
	newThreadID=winUser.getWindowThreadProcessID(newHwnd)[1]
	return newThreadID!=api.getFocusObject().windowThreadID

	def __contains__(self,obj):
		if not obj.windowClassName.startswith("Internet Explorer_"):
			return False
		#Combo box lists etc are popup windows, so rely on accessibility hierarchi instead of window hierarchi for those.
		#However only helps in IE8.
		if obj.windowStyle&winUser.WS_POPUP:
			parent=obj.parent
			obj.parent=parent
			while parent and parent.windowHandle==obj.windowHandle:
				newParent=parent.parent
				parent.parent=newParent
				parent=newParent
			if parent and parent.windowClassName.startswith('Internet Explorer_'):
				obj=parent
		if obj.windowHandle==self.rootDocHandle:
			return True
		if winUser.isDescendantWindow(self.rootDocHandle,obj.windowHandle):
			return True
		return False

def processForegroundWinEvent(window,objectID,childID):
	"""checks to see if the foreground win event is not the same as the existing focus or any of its parents, 
	then converts the win event to an NVDA event (instanciating an NVDA Object) and then checks the NVDAObject against the existing focus object. 
	If all is ok it queues the foreground event to NVDA and returns True.
	@param window: a win event's window handle
	@type window: integer
	@param objectID: a win event's object ID
	@type objectID: integer
	@param childID: a win event's child ID
	@type childID: integer
	@returns: True if the foreground was processed, False otherwise.
	@rtype: boolean
	"""
	#Ignore foreground events on windows that aren't the current foreground window
	if window!=winUser.getForegroundWindow():
		return False
	# If there is a pending gainFocus, it will handle the foreground object.
	oldFocus=eventHandler.lastQueuedFocusObject
	#If this foreground win event's window is an ancestor of the existing focus's window, then ignore it
	if isinstance(oldFocus,NVDAObjects.window.Window) and winUser.isDescendantWindow(window,oldFocus.windowHandle):
		return False
	#If the existing focus has the same win event params as these, then ignore this event
	if isinstance(oldFocus,NVDAObjects.IAccessible.IAccessible) and window==oldFocus.event_windowHandle and objectID==oldFocus.event_objectID and childID==oldFocus.event_childID:
		return False
	#Notify appModuleHandler of this new foreground window
	appModuleHandler.update(winUser.getWindowThreadProcessID(window)[0])
	#If Java access bridge is running, and this is a java window, then pass it to java and forget about it
	if JABHandler.isRunning and JABHandler.isJavaWindow(window):
		JABHandler.event_enterJavaWindow(window)
		return True
	#Convert the win event to an NVDA event
	NVDAEvent=winEventToNVDAEvent(winUser.EVENT_SYSTEM_FOREGROUND,window,objectID,childID,useCache=False)
	if not NVDAEvent:
		return False
	eventHandler.queueEvent(*NVDAEvent)
	return True

	def _get_isAlive(self):
		if self.isLoading:
			return True
		root=self.rootNVDAObject
		if not root:
			return False
		if not winUser.isWindow(root.windowHandle):
			return False
		if root.appModule.appName.startswith('wwahost') and not winUser.isDescendantWindow(winUser.getForegroundWindow(),root.windowHandle):
			# #4572: When a wwahost hosted app is in the background it gets suspended and all COM calls freeze.
			# Therefore we don't have enough info to say whether its dead or not. We assume it is alive until we can get a better answer.
			return True
		try:
			if not root.IAccessibleRole:
				# The root object is dead.
				return False
		except watchdog.CallCancelled:
			# #1831: If the root object isn't responding, treat the buffer as dead.
			# Otherwise, we'll keep querying it on every focus change and freezing.
			return False
		states=root.states
		if controlTypes.STATE_EDITABLE in states:
			return False
		return True

	def __contains__(self,obj):
		return winUser.isDescendantWindow(self.rootNVDAObject.windowHandle, obj.windowHandle)

	def __contains__(self,obj):
		if not (isinstance(obj,NVDAObjects.IAccessible.IAccessible) and isinstance(obj.IAccessibleObject,IAccessibleHandler.IAccessible2)) or not obj.windowClassName.startswith('Mozilla') or not winUser.isDescendantWindow(self.rootNVDAObject.windowHandle,obj.windowHandle):
			return False
		if self.rootNVDAObject.windowHandle==obj.windowHandle:
			ID=obj.IA2UniqueID
			try:
				self.rootNVDAObject.IAccessibleObject.accChild(ID)
			except COMError:
				return ID==self.rootNVDAObject.IA2UniqueID

		return not self._isNVDAObjectInApplication(obj)