what does "subclassing window" mean?

[lobanovski]

hi all, i do not get a meaning of this saying "subclass a window", but it's used quite often when i deal with wtl, or any other "tricky stuff"... :( what does this mean??? alex debug - is my life style

[Mike Dimmick]

Basically, it means replacing the window's existing window procedure with another one (typically one you've written). This allows you to change certain aspects of the window's behaviour, while passing other events onto the original window procedure. You might do this if, say, you wanted to trap certain keypresses in an edit control, or draw a button differently, but reuse the general behaviour of the control.