stability of widget API

[Tim Graham]

I recently updated the following patch regarding creating custom widgets:

https://code.djangoproject.com/attachment/ticket/11185/11185.diff

It mentions:

Interfaces of classes :class:`~django.forms.widgets.Widget` and  :class:`~django.forms.widgets.MultiWidget` are still in flux, therefore -  please take care to test all of your custom widgets when upgrading Django. As far as I know, it's our practice *not* to document APIs that may change, however, I'm not sure there's anything in the patch that is subject to change.  Could someone give a quick look?  Thanks!