Search notes:

Oracle: PROPS$

PROP$ vs X$PROP

select
   nvl(x.name, b.name) name,
   substr(x.value$, 1, 30)      val_x$,
   substr(b.value$, 1, 30)      val_base_tab
from
   sys.x$props  x                              full outer join
   sys.props$   b on x.name = b.name;

See also

props$ is created in $ORACLE_HOME/rdbms/admin/dcore.bsq.

sys.dbms_registry_sys.delete_props_data(…)

The fixed table x$props.

catmetviews_mig.sql