@workInProgress
@ngdoc overview
@name angular.attrMarkup

@description
Attribute markup extends the angular compiler in a very similar way as {@link angular.markup} except
that it allows you to modify the state of the attribute text rather then the contest of a node.

<pre>
angular.attrMarkup('extraClass', function(attrValue, attrName, element){
  if (attrName == 'additional-class') {
    element.addClass(attrValue);
  }
});
</pre>
