directive('tabs', function() {
return {
            restrict: 'E',
            transclude: true,
            scope: {},
            controller: ["$scope", function($scope) {
                var panes = $scope.panes = [];                
                $scope.select = function(pane) {
                    angular.forEach(panes, function(pane) {
                        pane.selected = false;
                    });
                    pane.selected = true;
                }
 
                this.addPane = function(pane) {
                    if(panes.length == 0) $scope.select(pane);
                    panes.push(pane);
                }
            }],
            template: '
' +                '
' +                '
' +                '{{pane.title}}' +//ng-click="select(pane)"
                '
' +                '
' +                '
' +                '
',
            replace: true
        };
    }).
    directive('pane', function() {        return {            require: '^tabs',//
            restrict: 'E',
            transclude: true,
            scope: {
                title: '@'
            },
            link: function(scope, element, attrs, tabsCtrl) {
                 
                tabsCtrl.addPane(scope);//这里为什么传scope参数呢
            },
            template: '
' +//ng-class="{active: selected}"怎么理解呢
                '
',
            replace: true
        };
    })