function Sort(commandID, compareFn, events, automaticFn) {
        this._commandID = commandID;
        this._compareFn = compareFn;
        this._events    = events;
    }
@constructor
@param {string} commandID A valid command identifier.
@param {function(File, File): number} compareFn A valid sort
     function (see register for a longer explanation).
@param {string} events Space-separated WorkingSetSort possible events
     ending with ".sort".