Neither Win nor WinCE port implements asynchronous spellchecking. Win: Source/WebKit/win/WebCoreSupport/WebEditorClient.h virtual void requestCheckingOfString(WTF::PassRefPtr<WebCore::TextCheckingRequest>) override { } WinCE: Source/WebKit/wince/WebCoreSupport/EditorClientWinCE.h virtual void requestCheckingOfString(WTF::PassRefPtr<WebCore::TextCheckingRequest>) override { }