Fixed #8299 -- Clarified the ModelAdmin.form option. Also added an in…

…ner Meta class to the ModelForm example in adding custom validation to the admin. Thanks jarrow for the report and initial patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8395 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/admin.txt

@@ -72,9 +72,14 @@ Example::
 ``form``
 ~~~~~~~~
 
-The default ``forms.ModelForm`` class used to generate the form on the
-add/change pages for models. You can easily change this to your own
-``ModelForm`` to override the default form behavior of the add/change pages.
+By default a ``ModelForm`` is dynamically created for your model. It is used
+to create the form presented on both the add/change pages. You can easily
+provide your own ``ModelForm`` to override any default form behavior on the
+add/change pages.
+
+For an example see the section `Adding custom validation to the admin`_.
+
+.. _Adding custom validation to the admin: #adding-custom-validation-to-the-admin
 
 ``fieldsets``
 ~~~~~~~~~~~~~
@@ -617,6 +622,9 @@ needed. Now within your form you can add your own custom validation for
 any field::
 
     class MyArticleAdminForm(forms.ModelForm):
+        class Meta:
+            model = Article
+
         def clean_name(self):
             # do something that validates your data
             return self.cleaned_data["name"]