N is mandatory and sets the length of the control in average character
value is the current value represented by the slider in the range min
to max. This value can also be accessed by a call-back function whilst
the slider is being moved.
option can be set to the keyword vertical to provide an alternative to
the default which is a horizontal slider.
The slider will respond to the arrow keys on the keyboard.
The value returned by clearwin_info@('LATEST_VARIABLE') can also be used with