flStyle (ULONG) - input
This can be any of the standard class styles (CS_*) in addition to any class-specific styles that are defined. These styles can be augmented when a window of this class is created.
A public window class is created if the CS_PUBLIC style is specified, otherwise a private class is created. The CS_PUBLIC style must only be specified for the shell process.
Public classes are available for creating windows from any process. Private classes are only available to the registering process.