Fw: Polymorphism question

I am new to PHP but 10 years in C++ One of the cool/powerful things you can do in C++ is the following: class DrawDialog { public: ... virtual Draw(); // implementation draws a plain dialog box }; class DrawStyleDialog : public DrawPlainDialog { public: ... virtual Draw(); // implementation draws better dialog based on some parameters }; Somewhere in my code I have a function like: void ShowGUI( DrawDialog& dd ) { dd.Draw(); } ShowGUI can be called with any object that is derived from DrawDialog, obviously. Only code that calls ShowGUI must be changed when a new implementation of DrawDialog is used. This feature of C++ to have a base class pointer (or reference) be able to access derived class functionality is not something I've seen in any PHP documentation. Does it exist, and if not is there a workaround for this highly desirable feature? TIA Rich PS Can anyone point me to the most comprehensive OOP documentation for PHP? ----------