Fixed another typo in custom model field documentation.

than disappearing if they take on the old default value.

In addition, try to avoid returning values as positional arguments; where

possible, return values as keyword arguments for maximum future compatability.

possible, return values as keyword arguments for maximum future compatibility.

Of course, if you change the names of things more often than their position

in the constructor's argument list, you might prefer positional, but bear in

mind that people will be reconstructing your field from the serialized version