See whether the focus control wants to handle the specified message. It is assumed that if the focus control has a public or non-public method of the given name, it takes the supplied arguments and returns boolean. Call it and return what it returns. Special case: if the focus control is 'this', that is, the recipient xWindow has focus, just return false. This is because this method is called from, say, the implementation of OnDisplayUndo, to see whether some (other) focus control wants to handle the message. Returning false allows the correct default implementation of OnDisplayUndo when no (other) focused control wants to do it. Calling OnDisplayUndo on the focus control, on the other hand, leads to a stack overflow, since the first thing this.OnDisplayUndo does is to call FocusControlHandlesMessage again!