code: function highlight(node, ok) {
          if (!node) return;
          if (self.options.markParen) {
            self.options.markParen(node, ok);
          }
          else {
            node.style.fontWeight = "bold";
            node.style.color = ok ? "#8F8" : "#F88";
          }
        }
docs: give the relevant nodes a colour.