public boolean appendVerifyKeyListener(VerifyKeyListener verifyKeyListener) {
if (fContentAssistSubjectControl != null)
return fContentAssistSubjectControl.appendVerifyKeyListener(verifyKeyListener);
else if (fViewer instanceof ITextViewerExtension) {
ITextViewerExtension extension= (ITextViewerExtension)fViewer;
extension.appendVerifyKeyListener(verifyKeyListener);
return true;
} else {
StyledText textWidget= fViewer.getTextWidget();
if (Helper.okToUse(textWidget)) {
textWidget.addVerifyKeyListener(verifyKeyListener);