case WM_UNDOCUMENTED: ...
Interesting discovery. A little background:
I was attempting to streamline my message loop so that it ignores unwanted messages. So I added all the desired messages to the "wanted" list, and ran the program.
Result? The program would not close.
So I decided to print out all messages not on my list. There were four to speak of, namely:
It turns out, the first three were my problem. The 'x' was in the non-client area.
But the fourth one, though apparently harmless, was nowhere to be found in any of my header files. So with a little experimenting, it became apparent that the last message was sent whenever the mouse hovers over the title bar. Question: does anyone else have this value defined in their headers? Try this:
#define FOUND_IT 280
If the compiler complains, then you do.
It may just be a newer message than my compiler's documentation covers...but interesting nonetheless, and I have added a new entry to my winuser.h!