docs(changelog, migration): add BC notice for allowed form name values

Introduced by angular@94533e5

Closes angular#13771

Author: Narretz

CHANGELOG.md

@@ -1519,6 +1519,34 @@ describe('$q.when', function() {
 });
 ```
 
+- **form:** Due to [94533e57](https://github.com/angular/angular.js/commit/94533e570673e6b2eb92073955541fa289aabe02),
+  the `name` attribute of `form` elements can now only contain characters that can be evaluated as part
+  of an Angular expression. This is because Angular uses the value of `name` as an assignable expression
+  to set the form on the `$scope`. For example, `name="myForm"` assigns the form to `$scope.myForm` and
+  `name="myObj.myForm"` assigns it to `$scope.myObj.myForm`.
+
+  Previously, it was possible to also use names such `name="my:name"`, because Angular used a special setter
+  function for the form name. Now the general, more robust `$parse` setter is used.
+
+  The easiest way to migrate your code is therefore to remove all special characters from the `name` attribute.
+
+  If you need to keep the special characters, you can use the following directive, which will replace
+  the `name` with a value that can be evaluated as an expression:
+
+  ```js
+  angular.module('myApp').directive('form', function() {
+    return {
+      restrict: 'E',
+      priority: 1000,
+      compile: function(element, attrs) {
+        var unsupportedCharacter = ':' // change accordingly
+        if (attrs.name && attrs.name.indexOf(unsupportedCharacter) > 0) {
+          attrs.$set('name', 'this["' + attrs.name + '"]');
+        }
+      }
+    };
+  });
+  ```
 
 <a name="1.4.3"></a>
 # 1.4.3 foam-acceleration (2015-07-15)

docs/content/guide/migration.ngdoc

@@ -473,6 +473,38 @@ ngModelCtrl.$formatters.push(function(value) {
 });
 ```
 
+
+### form
+
+Due to [94533e57](https://github.com/angular/angular.js/commit/94533e570673e6b2eb92073955541fa289aabe02),
+the `name` attribute of `form` elements can now only contain characters that can be evaluated as part
+of an Angular expression. This is because Angular uses the value of `name` as an assignable expression
+to set the form on the `$scope`. For example, `name="myForm"` assigns the form to `$scope.myForm` and
+`name="myObj.myForm"` assigns it to `$scope.myObj.myForm`.
+
+Previously, it was possible to also use names such `name="my:name"`, because Angular used a special setter
+function for the form name. Now the general, more robust `$parse` setter is used.
+
+The easiest way to migrate your code is therefore to remove all special characters from the `name` attribute.
+
+If you need to keep the special characters, you can use the following directive, which will replace
+the `name` with a value that can be evaluated as an expression:
+
+```js
+angular.module('myApp').directive('form', function() {
+  return {
+    restrict: 'E',
+    priority: 1000,
+    compile: function(element, attrs) {
+      var unsupportedCharacter = ':' // change accordingly
+      if (attrs.name && attrs.name.indexOf(unsupportedCharacter) > 0) {
+        attrs.$set('name', 'this["' + attrs.name + '"]');
+      }
+    }
+  };
+});
+```
+
 ### Templating (`ngRepeat`, `$compile`)
 
 #### ngRepeat