  * **admin.E011**: The value of ``fieldsets[n][1]`` must contain the key
    ``fields``.
  * **admin.E012**: There are duplicate field(s) in ``fieldsets[n][1]``.
  * **admin.E013**: ``fields[n]/fieldsets[n][m]`` cannot include the
    ``ManyToManyField`` ``<field name>``, because that field manually specifies a
    relationship model.
  * **admin.E014**: The value of ``exclude`` must be a list or tuple.
  * **admin.E015**: The value of ``exclude`` contains duplicate field(s).
  * **admin.E016**: The value of ``form`` must inherit from ``BaseModelForm``.
  * **admin.E017**: The value of ``filter_vertical`` must be a list or tuple.
 
</s> remove * **admin.E003**: The value of ``raw_id_fields[n]`` must be a ``ForeignKey`` or
  ``ManyToManyField``.
 </s> add * **admin.E003**: The value of ``raw_id_fields[n]`` must be a foreign key or
  a many-to-many field. </s> remove   ``<field name>``, which must not be a ``DateTimeField``, ``ForeignKey`` or
  ``ManyToManyField``.
 </s> add   ``<field name>``, which must not be a ``DateTimeField``, a foreign key or a
  many-to-many field. </s> remove   be a ``ManyToManyField``.
 </s> add   be a many-to-many field. </s> remove   ``ManyToManyField``.
 </s> add   many-to-many field. </s> remove                 "The value of 'fieldsets[1][1][\"fields\"]' cannot include the ManyToManyField "
                "'authors', because that field manually specifies a relationship model.",
 </s> add                 "The value of 'fieldsets[1][1][\"fields\"]' cannot include the many-to-many field "
                "'authors' because that field manually specifies a relationship model.",
  many-to-many field ``<field name>``, because that field manually specifies a
  * **admin.E011**: The value of ``fieldsets[n][1]`` must contain the key
    ``fields``.
  * **admin.E012**: There are duplicate field(s) in ``fieldsets[n][1]``.
  * **admin.E013**: ``fields[n]/fieldsets[n][m]`` cannot include the
  many-to-many field ``<field name>``, because that field manually specifies a
    relationship model.
  * **admin.E014**: The value of ``exclude`` must be a list or tuple.
  * **admin.E015**: The value of ``exclude`` contains duplicate field(s).
  * **admin.E016**: The value of ``form`` must inherit from ``BaseModelForm``.
  * **admin.E017**: The value of ``filter_vertical`` must be a list or tuple.
keep keep keep keep replace keep keep keep keep keep
 Refs #24227 -- Replaced M2M isinstance checks by field.many_to_many

Thanks Markus Holtermann, Collin Anderson and Tim Graham for the reviews. 
docs/ref/checks.txt