title: Angular $watch does not fire any event in my directive
body: <p>i try to update an elements content depending on the attribute value of my custom directive. the code below performs well but only once on site-load. dynamic updates on the attribute value do not fire any event. what do i do wrong?</p>
  
  <p>markup inside ng-repeat (match in matches):</p>
  
  <pre><code>&lt;div ng-tipp-result="[[getIconClass(match)]]"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>directive:</p>
  
  <pre><code>myApp.directive('ngTippResult', function() {
      return {
          restrict: 'A',
          link: function(scope, elem, attrs) {
              var content = "s";
  
              scope.$watch(attrs.ngTippResult, function(v){
                  switch(v){
                      case 1: content = '&lt;i class="icon-circle"&gt;&lt;/i&gt;';break;
                      case 2: content = '&lt;i class="icon-X"&gt;&lt;/i&gt;';break;
                      case 3: content = '&lt;i class="icon-Y"&gt;&lt;/i&gt;';break;
                      case 4: content = '&lt;i class="icon-Z"&gt;&lt;/i&gt;';break;
                      case 5: content = '&lt;i class="icon-ok"&gt;&lt;/i&gt;';break;
                      case 6: content = '&lt;i class="icon-minus"&gt;&lt;/i&gt;';break;
                  }
  
                  elem.html(content);
              });
          }
      };
  });
  </code></pre>
  
  <p><strong>Edit:</strong></p>
  
  <p>using the attributes name as string solved the problem but caused another, i ran into a infinit digest loop with the code above.</p>
  
  <pre><code>&lt;li ng-repeat="match in matches"&gt;
      &lt;i class="pull-right [[getIconClass(match)]]"&gt;&lt;/i&gt;
  &lt;/li&gt;
  </code></pre>
  
  <p>getIconClass is a controller method which returns values from 1 to 6 depending on match.</p>