code: function() {
      this.skipSpacesAndComments();
      this.expect('(');
      this.skipSpacesAndComments();
      var node = new nodes.Feature(this.interpolate());
      this.skipSpacesAndComments();
      this.accept(':')
      this.skipSpacesAndComments();
      this.inProperty = true;
      node.expr = this.list();
      this.inProperty = false;
      this.skipSpacesAndComments();
      this.expect(')');
      this.skipSpacesAndComments();
      return node;
    }
docs: '(' ident ( ':'? expression )? ')'