@uml @override
@uml @override
@uml The {@link ParseTreeVisitor} needs a double dispatch method.
@uml Return the combined text of all leaf nodes. Does not get any off-channel tokens (if any) so won't return whitespace and comments if they are sent to parser on hidden channel.
@uml Specialize toStringTree so that it can print out more information based upon the parser.
TODO add interface description