Document that ModelForm isn't actually a subclass of Form

[Haydar Al-Rikabi]

In the ​Django docs, I've read the following statement:
All form classes are created as subclasses of django.forms.Form, including the ModelForm, which you encounter in Django’s admin.

I believe that the above statement is wrong because as the Django project on Github does not show that ModelForm is a subclass of django.forms.Form.

in /django/forms/models.py the class ModelForm is subclass of BaseModelForm which is also a subclass of BaseForm (located in /django/forms/forms.py).
in /django/forms/forms.py the class Form is a subclass of BaseForm.

So, as you can see, both django.forms.Form and django.forms.ModelForm are subclasses of BaseForm, but ModelForm is not a subclass of Form as the docs state.

[Tim Graham]

​PR

[GitHub <noreply@…>]

In ff61a25:

Fixed #29107 -- Doc'd that ModelForm doesn't actually inherit from Form.

[Tim Graham <timograham@…>]

In 29dd7dcd:

[2.0.x] Fixed #29107 -- Doc'd that ModelForm doesn't actually inherit from Form.

Backport of ff61a250815d32ff185501a5afef0245fec7d878 from master