code: function(){
      var type = this.expect('atrule').val
        , node = new nodes.Atrule(type)
        , tok;
      this.skipSpacesAndComments();
      node.segments = this.selectorParts();
      this.skipSpacesAndComments();
      tok = this.peek().type;
      if ('indent' == tok || '{' == tok || ('newline' == tok
        && '{' == this.lookahead(2).type)) {
        this.state.push('atrule');
        node.block = this.block(node);
        this.state.pop();
      }
      return node;
    }
docs: atrule selector? block?