Allows to set the value for that field. Applies the modification by loading the new value in the current value. The modification is applied only if valid. Set the description. The input string should not be null.
Nothing is done if the string is null.
This method register objects which will be notified when this field value will be changed by the user. The class must implement an PrefNotify interface. This method removes a registered notify class. If classname is null, false is returned. This returns the list of classes that will be notified when the user changes this field.