Fixed #8861 -- Added note on the availability of ModelForm.instance. Thanks to Ramiro Morales for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11097 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/ref/contrib/admin/index.txt

@@ -870,7 +870,7 @@ Adding custom validation to the admin
 -------------------------------------
 
 Adding custom validation of data in the admin is quite easy. The automatic admin
-interfaces reuses :mod:`django.forms`, and the ``ModelAdmin`` class gives you
+interface reuses :mod:`django.forms`, and the ``ModelAdmin`` class gives you
 the ability define your own form::
 
     class ArticleAdmin(admin.ModelAdmin):
@@ -890,7 +890,9 @@ any field::
 
 It is important you use a ``ModelForm`` here otherwise things can break. See the
 :ref:`forms <ref-forms-index>` documentation on :ref:`custom validation
-<ref-forms-validation>` for more information.
+<ref-forms-validation>` and, more specifically, the
+:ref:`model form validation notes <overriding-modelform-clean-method>` for more
+information.
 
 .. _admin-inlines:
 

docs/topics/forms/modelforms.txt

@@ -397,16 +397,26 @@ to be rendered first, we could specify the following ``ModelForm``::
     ...         model = Book
     ...         fields = ['title', 'author']
 
+.. _overriding-modelform-clean-method:
 
 Overriding the clean() method
 -----------------------------
 
 You can override the ``clean()`` method on a model form to provide additional
-validation in the same way you can on a normal form. However, by default the
-``clean()`` method validates the uniqueness of fields that are marked as
-``unique``, ``unique_together`` or ``unique_for_date|month|year`` on the model.
-Therefore, if you would like to override the ``clean()`` method and maintain the
-default validation, you must call the parent class's ``clean()`` method.
+validation in the same way you can on a normal form.
+
+In this regard, model forms have two specific characteristics when compared to
+forms:
+
+By default the ``clean()`` method validates the uniqueness of fields that are
+marked as ``unique``, ``unique_together`` or ``unique_for_date|month|year`` on
+the model.  Therefore, if you would like to override the ``clean()`` method and
+maintain the default validation, you must call the parent class's ``clean()``
+method.
+
+Also, a model form instance bound to a model object will contain a
+``self.instance`` attribute that gives model form methods access to that
+specific model instance.
 
 Form inheritance
 ----------------