An application that registers a window class also can support its own set of styles for windows of that class. Standard window styles-for example, WS_VISIBLE and WS_SYNCPAINT-still apply to these windows. A window style is a 32-bit integer, and only the high 16 bits are used for the standard window styles; an application can use the low 16 bits for custom styles specific to a window class.

The operating system has unique window styles for all preregistered window classes. Styles such as FS_BORDER and BS_PUSHBUTTON are processed by the window procedure for the corresponding class. This means that an application can build the support for its own window styles into the window procedure for its private class. A window style designed for one window class will not work with another window class.