I never knew the existence of this hotkey

F13 is the PrintScreen (PrtScn) button. I think the original poster is cryptically pointing out a hotkey combination that prints the active window into your clipboard (instead of the entire screen). However, this can be done using the simpler Alt-PrtScn. To review:

* PrtScn: prints the whole screen into your clipboard

* Alt-PrtScn: prints the active window into your clipboard

* Ctrl-Alt-PrtScn: same as Alt-PrtScn

Presumably this functionality is only available to users of certain vintage keyboards: http://www.9999hp.net/keyboard/temp/1397003-big.jpg

:D I posted this as a joke. One of my coworker got me searching on google by mistrust. It took me at least 2 minutes before I realize there was no F13 key.