slider.vertical()
sl.vertical(true | false | () )
Toggles the slider from a vertical to a horizontal display or vice versa.
The effect is the same as shift-clicking the slider's title bar.
Like all functions of this kind, the "vertical()" method can be called
in three ways: without a parameter, in which case it returns the
actual status of the menu as a boolean, or with one parameter:
true or false, in which case it c$sets it.
Toggling can be done by
sl.vertical ( ! sl.vertical() )