angularjs指令的代码，看不懂，求高手解释下？

Question

angular.module('cnodejs.directives').directive(

  // Collection-repeat image recycling while loading

  // https://github.com/driftyco/ionic/issues/1742

  'resetImg', function ($document) {

    return {

      restrict: 'A',

      link: function($scope, $element, $attributes) {

        var applyNewSrc = function (src) {

          var newImg = $element.clone(true);

          newImg.attr('src', src);

          $element.replaceWith(newImg);

          $element = newImg;

        };

        $attributes.$observe('src', applyNewSrc);

        $attributes.$observe('ngSrc', applyNewSrc);

      }

    };

  }

);