Create single text index on multiple columns in multiple tables in 10G

Hello, everyone,

I met a problem related to Oracle TEXT in 10G.

I am going to Create single text index on multiple columns in multiple tables in 10G. I knew, "Create single text index on multiple columns in multiple tables" is impossible in 8i and 9i, but people told me we can do that in 10G, but they don't know how to do it.

I read the documentation of 10G of "text application developer" amd
"text reference", I created preference and attributes as follows:
===================================
ctx_ddl.create_preference('MY_MULTI','MULTI_COLUMN_DATASTORE');
ctx_ddl.set_attribute('MY_MULTI', 'COLUMNS','foo,bar,zoo,jar');
ctx_ddl.set_attribute('MY_MULTI','FILTER',',,Y');
===================================

But I can't go further, for example, I use the following syntax to create index on 2 columns (column name: clob1, clob2):

========================================
CREATE INDEX clob_index_1 ON tablea(clob1, clob2)
INDEXTYPE IS CTXSYS.CONTEXT;
=======================================

I want to search clob data type which is stored in the table columns,
I got the following error message:

ERROR at line 1:
ORA-29851: cannot build a domain index on more than one column

Any suggestions or advice are highly appreciated.

Thanks very much in advance.

Gary