How to catch DRG errors dealing with Oracle Text

Dear Folks,

I want to know how to catch exceptions using DRG error code when dealing with Oracle text.

e.g.

BEGIN

   Ctx_Ddl.Create_Preference('MY_SEARCH_STORAGE', 'BASIC_STORAGE');

END;

When 'MY_SEARCH_STORAGE' preference already exists, the above code segment raises the below error.

ORA-20000: Oracle Text error:

DRG-10701: preference USER1.MY_SEARCH_STORAGE already exists

ORA-06512: at "CTXSYS.DRUE", line 171

ORA-06512: at "CTXSYS.DRVLSB", line 19

ORA-06512: at "CTXSYS.CTX_DDL", line 23

ORA-06512: at line 2

I know we can easily catch ORA-20000 but is there a way that we can catch DRG-10701?

Thanks

Navinth