Edit in JSFiddle

var cvl = angular.module('cvl',[]);

cvl.directive('controllerExample',[function(){
    return {
            restrict: 'A',//attribute binding
            template: '<div ng-click"setRed" ng-class="controllerClass">Controller Click</div>',
            controller: ['$scope', '$element', function ($scope, $element) {
                $scope.setRed = function(){
                    //binds to ng-class in the template
                    $scope.controllerClass = 'red';
                }
            }]}}]);

cvl.directive('linkerExample',[ function(){
    return {
      restrict: 'A',
      template: '<div>Linker Click</div>',
      link: function(scope, element, attrs) {
        var btn = element;
        element.on('click', toggle);
        function toggle() {    
          element.addClass('red');
        }
      }}}]);

<h3>App</h3>
<div ng-app="cvl">
    <div controller-example=""></div>
    <div linker-example=""></div>
</div>

<br/>
<br/>
<br/>
<hr/>
    <h3>Explination</h3>
    <p><i>This script still requires some debugging. Have not wroked out how to efficiently debug in jsfiddle.</i></p>

    <p>Both examples do the same thing.</p>
    
    <p>Controllers in directives work the same way as controllers declared in the html.  The dependencies are a bit different.</p>

    <p>Linkers require more DOM manipulation.</p>
<p>
Another way to think of the relationship between linkers and controllers, though not usually shown in the beginner examples, is to use linkers to dynamically modify a base template, then pass the work over to controllers.  
    </p>
    <p>
        In my work with binding directives directly to xml documents, doing all the work in linkers has a performance increase when there is many instances of the directive invoked on the page. But no real difference when one instance of a directive is on a page.  In the example of an xml document with 100 users on the page, the controller method seemed to have poorer performance.  I did not formally benchmark and this may change between versions of AngularJs.</p>

red{
    color:red;
}