question: public static < T > String toString ( TreeDef < T > treeDef , T root , Function < ? super T , String > toString , String indent ) { StringBuilder builder = new StringBuilder ( ) ; builder . append ( toString . apply ( root ) ) ; builder . append ( "\n" ) ; toStringHelper ( treeDef , root , toString , indent , builder , indent ) ; return builder . toString ( ) ; }
target:  Converts the entire tree into a string-based representation.