code: public String debugPrint() {
          DebugPrintVisitor dpv = new DebugPrintVisitor(new StringBuilder(1000));
          visit(dpv);
          return dpv.toString();
      }
docs: Returns a debugging representation of the parse tree
  starting at this node.
  @return a very verbose indented printout of the tree.
  The format of each line is:  abs-pos  name position length [identifier]