minimal init.ora

my minimal init.ora has only 4 lines:

*.compatible='11.1.0.0.0'
*.control_files='/appl/oracle/oradata/BERX2/control01.ctl','/appl/oracle/oradata/BERX2/control02.ctl','/appl/oracle/oradata/BERX2/control03.ctl'
*.db_block_size=8192
*.db_name='BERX2'

where I have to check if I can omit the compatible. So it would be down to 3 lines. nice!
Without setting compatible, I get

ORA-00201: control file version 11.1.0.0.0 incompatible with ORACLE version
11.0.0.0.0
ORA-00202: control file: '/appl/oracle/oradata/BERX2/control01.ctl'

and a show parameter compatible gives

compatible                           string      11.0.0

strange, as the instance identifies itselve as

SQL> select version from v$instance;

VERSION
-----------------
11.1.0.7.0

So it seems the automatic value for compatible is derived only from the first Version number of v$instance.