Called with (cls, connection, extra_sql, post_funcs). extra_sql is a list (which can be appended to) of extra SQL statements to be run after the table is created. post_funcs functions are called with (cls, connection) after the table has been created. Those functions are not called simply when constructing the SQL.
Abstract classes can override this to customize issubclass().
This is invoked early on by abc.ABCMeta.__subclasscheck__(). It should return True, False or NotImplemented. If it returns NotImplemented, the normal algorithm is used. Otherwise, it overrides the normal algorithm (and the outcome is cached).
See the source for more information.