Specifically, the "RT" and "TR" operators.
"RT" represents "Related Term" and "TR" represents "Translated Term"
Just something to keep in mind if you, like a large number of people, assign all of your Region Templates with a "RT" prefix. Then, while troubleshooting, you find that the reciprocal produces the same error.
Unable to retrieve search results. Error generated when executing query '(((DEFINESCORE((rt), RELEVANCE * .01 + 1)) ))'. Unable to execute callable query 'CotsSearchQuery'. ORA-20000: Oracle Text error:
DRG-50857: oracle error in ctx_query.result_set
ORA-20000: Oracle Text error:
DRG-50901: text query parser syntax error on line 1, column 19
ORA-06512: at "CTXSYS.DRUE", line 160
ORA-06512: at "CTXSYS.CTX_QUERY", line 788
ORA-06512: at "DB_ADMIN.CONTENT_SEARCH", line 123
ORA-06512: at line 1
See here for the full list of OracleText CONTAINS Query Operators:
Oracle Text 11g Documentation
Not the most helpful of hints, but might save you some embarrassment :)