window.hide (window.frontMost ())
» true
There's always a frontmost window. Be careful not to script this with only the Quick Script and Fontier.root windows open because it will hide your Fontier.root window. To get the Fontier.root window back if that does happen, select its title
(usually "Frontier.root") from the Window menu.
Make sure the examples window is closed. Now type and execute:
window.hide ("examples")
» false
The Window wasn't open, therefore it couldn't be hidden.