IE: To tell Qbasic to go full screen or not.
You cannot do that as Windows blocks sending keys to the buffer using software.
Older computers used to be able to change the function keys, but not anymore.
_FULLSCREEN or _FULLSCREEN _OFF can do that in QB64.
You can do it with Windows API Libraries in QB64, but ALT + Enter already works without that!: http://www.qb64.net/wiki/index.php/Windows_Libraries#Hot_Keys_.28maximize.29