The WindowClass constants categorize windows into groups of like types. The grouping of windows facilitates the appropriate display (that is, both the look and the front-to-back ordering) and tracking of windows.
You can define a window's class using the function CreateNewWindow and obtain a window's class using the function GetWindowClass . However, a window's class cannot be altered once the window has been created.
Note that the ordering of the constants in the WindowClass enumeration reflects the window classes' relative front-to-back display order.
enum {
kAlertWindowClass = 1L,
kMovableAlertWindowClass = 2L,
kModalWindowClass = 3L,
kMovableModalWindowClass = 4L,
kFloatingWindowClass = 5L,
kDocumentWindowClass = 6L
};
typedef UInt32 WindowClass;