Default placeholder functions

Unlike pure virtual functions, default placeholder functions don't have to be overridden.

They offer minimal default actions or no actions at all. They serve as placeholders, where you can place code in your derived classes. For example, here's the definition of TWindow::EvLButtonDblClk:

inline void
TWindow::EvLButtonDblClk (uint modKeys, TPoint &)
{
 DefaultProcessing();
}

By default, EvLButtonDblClk calls DefaultProcessing to perform the default message processing for that message. In your own window class, you could override EvLButtonDblClk by defining it in your class response table. Your version of EvLButtonDblClk can provide some custom behavior that happens when the user clicks the left mouse button. You can also continue to provide the base class default processing by calling the base class version of the function.