docs(copy): mention ignoring non-enumerable properties

This also improves the example a bit:
- better code formatting
- initialization of `form` to an empty object
- avoid using `email`, which doesn't get coppied when invalid (and might confuse users)

Fixes #14853

Author: gkalpak

src/Angular.js

@@ -752,7 +752,13 @@ function arrayRemove(array, value) {
  * * If a destination is provided, all of its elements (for arrays) or properties (for objects)
  *   are deleted and then all elements/properties from the source are copied to it.
  * * If `source` is not an object or array (inc. `null` and `undefined`), `source` is returned.
- * * If `source` is identical to 'destination' an exception will be thrown.
+ * * If `source` is identical to `destination` an exception will be thrown.
+ *
+ * <br />
+ * <div class="alert alert-warning">
+ *   Only enumerable properties are taken into account. Non-enumerable properties (both on `source`
+ *   and on `destination`) will be ignored.
+ * </div>
  *
  * @param {*} source The source that will be used to make a copy.
  *                   Can be any type, including primitives, `null`, and `undefined`.
@@ -761,41 +767,42 @@ function arrayRemove(array, value) {
  * @returns {*} The copy or updated `destination`, if `destination` was specified.
  *
  * @example
- <example module="copyExample">
- <file name="index.html">
- <div ng-controller="ExampleController">
- <form novalidate class="simple-form">
- Name: <input type="text" ng-model="user.name" /><br />
- E-mail: <input type="email" ng-model="user.email" /><br />
- Gender: <input type="radio" ng-model="user.gender" value="male" />male
- <input type="radio" ng-model="user.gender" value="female" />female<br />
- <button ng-click="reset()">RESET</button>
- <button ng-click="update(user)">SAVE</button>
- </form>
- <pre>form = {{user | json}}</pre>
- <pre>master = {{master | json}}</pre>
- </div>
-
- <script>
-  angular.module('copyExample', [])
-    .controller('ExampleController', ['$scope', function($scope) {
-      $scope.master= {};
-
-      $scope.update = function(user) {
-        // Example with 1 argument
-        $scope.master= angular.copy(user);
-      };
+  <example module="copyExample">
+    <file name="index.html">
+      <div ng-controller="ExampleController">
+        <form novalidate class="simple-form">
+          <label>Name: <input type="text" ng-model="user.name" /></label><br />
+          <label>Age:  <input type="number" ng-model="user.age" /></label><br />
+          Gender: <label><input type="radio" ng-model="user.gender" value="male" />male</label>
+                  <label><input type="radio" ng-model="user.gender" value="female" />female</label><br />
+          <button ng-click="reset()">RESET</button>
+          <button ng-click="update(user)">SAVE</button>
+        </form>
+        <pre>form = {{user | json}}</pre>
+        <pre>master = {{master | json}}</pre>
+      </div>
+    </file>
+    <file name="script.js">
+      // Module: copyExample
+      angular.
+        module('copyExample', []).
+        controller('ExampleController', ['$scope', function($scope) {
+          $scope.master = {};
+
+          $scope.reset = function() {
+            // Example with 1 argument
+            $scope.user = angular.copy($scope.master);
+          };
 
-      $scope.reset = function() {
-        // Example with 2 arguments
-        angular.copy($scope.master, $scope.user);
-      };
+          $scope.update = function(user) {
+            // Example with 2 arguments
+            angular.copy(user, $scope.master);
+          };
 
-      $scope.reset();
-    }]);
- </script>
- </file>
- </example>
+          $scope.reset();
+        }]);
+    </file>
+  </example>
  */
 function copy(source, destination) {
   var stackSource = [];