      setting, if set. If the backend doesn't support tablespaces, this option is
      ignored.
  
  ``default_related_name``
  ------------------------
  
  .. attribute:: Options.default_related_name
  
 
</s> remove                 reconstruct_manager(model._default_manager)
 </s> add                 default_manager = copy.copy(model._default_manager)
                default_manager._set_creation_counter()

            # If the default manager doesn't have `use_in_migrations = True`,
            # shim a default manager so another manager isn't promoted in its
            # place. </s> remove ~~~~~~~~~~~~~~~~
 </s> add ----------------

.. attribute:: Model._default_manager </s> remove If the normal plain manager class (:class:`django.db.models.Manager`) is not
appropriate for your circumstances, you can force Django to use the same class
as the default manager for your model by setting the ``use_for_related_fields``
attribute on the manager class. This is documented fully below_.
 </s> add If the normal base manager class (:class:`django.db.models.Manager`) isn't
appropriate for your circumstances, you can tell Django which class to use by
setting :attr:`Meta.base_manager_name
<django.db.models.Options.base_manager_name>`.
``default_manager_name``
------------------------

.. attribute:: Options.default_manager_name

.. versionadded:: 1.10

The name of the manager to use for the model's
:attr:`~django.db.models.Model._default_manager`.

      setting, if set. If the backend doesn't support tablespaces, this option is
      ignored.
  
``default_manager_name``
------------------------

.. attribute:: Options.default_manager_name

.. versionadded:: 1.10

The name of the manager to use for the model's
:attr:`~django.db.models.Model._default_manager`.

  ``default_related_name``
  ------------------------
  
  .. attribute:: Options.default_related_name
  
keep keep add keep keep keep keep keep
 Fixed #10506, #13793, #14891, #25201 -- Introduced new APIs to specify models' default and base managers.

This deprecates use_for_related_fields.

Old API:

class CustomManager(models.Model):
    use_for_related_fields = True

class Model(models.Model):
    custom_manager = CustomManager()

New API:

class Model(models.Model):
    custom_manager = CustomManager()

    class Meta:
        base_manager_name = 'custom_manager'

Refs #20932, #25897.

Thanks Carl Meyer for the guidance throughout this work.
Thanks Tim Graham for writing the docs. 
docs/ref/models/options.txt