- rework the "controlling DDL sequences" documentation to refer mostly to the DDL object; this system is primarily useful in that case, and not for built-in objects.  Reference that the built-in case is not really viable right now. References #3442.
- rework the "controlling DDL sequences" documentation to
refer mostly to the DDL object; this system is primarily useful
in that case, and not for built-in objects.  Reference that
the built-in case is not really viable right now. References #3442.

sandan/sqlalchemy,Akrog/sqlalchemy,brianv0/sqlalchemy,zzzeek/sqlalchemy,ThiefMaster/sqlalchemy,brianv0/sqlalchemy,robin900/sqlalchemy,elelianghh/sqlalchemy,davidjb/sqlalchemy,Akrog/sqlalchemy,robin900/sqlalchemy,hsum/sqlalchemy,epa/sqlalchemy,hsum/sqlalchemy,wujuguang/sqlalchemy,davidfraser/sqlalchemy,276361270/sqlalchemy,epa/sqlalchemy,j5int/sqlalchemy,j5int/sqlalchemy,EvaSDK/sqlalchemy,wujuguang/sqlalchemy,elelianghh/sqlalchemy,276361270/sqlalchemy,sqlalchemy/sqlalchemy,sandan/sqlalchemy,graingert/sqlalchemy,itkovian/sqlalchemy,itkovian/sqlalchemy,davidfraser/sqlalchemy,graingert/sqlalchemy,monetate/sqlalchemy,davidjb/sqlalchemy,bdupharm/sqlalchemy,monetate/sqlalchemy,EvaSDK/sqlalchemy,ThiefMaster/sqlalchemy,bdupharm/sqlalchemy