Holy cow, I wrote a book!
There are 64 bits of styles in the parameters to CreateWindowEx.
Which ones belong to whom?
Windows defines the meanings of the high word of the dwStyle
parameter and all of the bits in the dwExStyle parameter.
The low 16 bits of the dwStyle parameter are defined by
the implementor of the window class (by the person who calls
In Windows 95, we found several apps that noticed that some
bits in the dwExStyle weren't being used, so they decided
to use them for themselves. Then when we added meanings to
those bits (such as WS_EX_TOOLWINDOW), these programs started
So don't be like those programs. Don't use bits that don't
belong to you.