code: function() {
      var node = this.expression();
  
      while (this.accept(',')) {
        if (node.isList) {
          list.push(this.expression());
        } else {
          var list = new nodes.Expression(true);
          list.push(node);
          list.push(this.expression());
          node = list;
        }
      }
      return node;
    }
docs: expression (',' expression)*