How to use Rhino command sub-options _ abbreviations?

For example below, O is underscored for “On”, how to activate the shortcut? I tried -O - Enter but nothing happens

Command: SmartTrack
SmarkTrack is on. New Value (On Off Toggle):

_SmartTrack O
_SmartTrack F
_SmartTrack T

should do it.


My bad -O - Enter does work. I was probably drunk for a second