Fixed #24250 -- Corrected mistakes in FormMixin docs.

    A mixin class that provides facilities for creating and displaying forms.

    **Mixins**

    * :class:`django.views.generic.base.ContextMixin`

    **Methods and Attributes**

    .. attribute:: initial

        Renders a response, providing the invalid form as context.

    .. method:: get_context_data(**kwargs)

        Populates a context containing the contents of ``kwargs``.

    **Context**

    * ``form``: The form instance that was generated for the view.

    .. note::

        Views mixing ``FormMixin`` must provide an implementation of

        :meth:`form_valid` and :meth:`form_invalid`.

ModelFormMixin

--------------