  should raise either a ``ValueError`` if the ``value`` is of the wrong sort (a
  list when you were expecting an object, for example) or a ``TypeError`` if
  your field does not support that type of lookup. For many fields, you can get
  by with handling the lookup types that need special handling for your field
  and pass the rest to the :meth:`get_db_prep_lookup` method of the parent class.
  
  If you needed to implement ``get_db_prep_save()``, you will usually need to
  implement ``get_prep_lookup()``. If you don't, ``get_prep_value`` will be
  called by the default implementation, to manage ``exact``, ``gt``, ``gte``,
  ``lt``, ``lte``, ``in`` and ``range`` lookups.
 
</s> remove ``get_db_prep_value``, you shouldn't need to implement this method
 </s> add :meth:`.get_db_prep_value`, you shouldn't need to implement this method </s> remove :meth:`get_db_prep_value` is the method where those conversions should
 </s> add :meth:`.get_db_prep_value` is the method where those conversions should </s> remove If you use :class:`~django.db.models.SubfieldBase`, :meth:`to_python`
 </s> add If you use :class:`~django.db.models.SubfieldBase`, :meth:`.to_python` </s> remove parameters (which is implemented by ``get_db_prep_value``).
 </s> add parameters (which is implemented by :meth:`.get_db_prep_value`).
and pass the rest to the :meth:`.get_db_prep_lookup` method of the parent class.
  should raise either a ``ValueError`` if the ``value`` is of the wrong sort (a
  list when you were expecting an object, for example) or a ``TypeError`` if
  your field does not support that type of lookup. For many fields, you can get
  by with handling the lookup types that need special handling for your field
and pass the rest to the :meth:`.get_db_prep_lookup` method of the parent class.
  
  If you needed to implement ``get_db_prep_save()``, you will usually need to
  implement ``get_prep_lookup()``. If you don't, ``get_prep_value`` will be
  called by the default implementation, to manage ``exact``, ``gt``, ``gte``,
  ``lt``, ``lte``, ``in`` and ``range`` lookups.
keep keep keep keep replace keep keep keep keep keep
 Fixed #15308 -- Sphinx/reST fixes for the Custom Model Fields docs.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15547 bcc190cf-cafb-0310-a4f2-bffc1f526a37 
docs/howto/custom-model-fields.txt