question: private void toString ( StringBuilder acc , int prec , boolean expand ) { if ( this . meta != null && ! expand ) { acc . append ( this . meta ) ; return ; } boolean paren = op . getPrec ( ) < prec ; if ( paren ) acc . append ( '(' ) ; toString ( acc , expand ) ; if ( paren ) acc . append ( ')' ) ; }
target:  This handles adding parens, as necessary.