First argument is optional (allowed to be NULL). See also the annotation "_In_opt_". Reference: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-postmessagea
First argument is optional (allowed to be NULL). See also the annotation "_In_opt_". Reference: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-postmessagea