Just committed the ability to do "full text" searching in the TACTIC expression language in 4.4 alpha.
@SOBJECT(test/type['keywords','@@','fast red car'])
This can be mixed with other search criteria:
@SOBJECT(test/type['keywords','@@','fast red car']['media_type','image'])
This will make use of the underlying database's full text search. At present, the operator used is '@@' simply because it is used in PostgreSQL. This doesn't seem to be a standard operator, but will work in the meantime.
Full text search had previously been implemented for PostgreSQL and SQLServer so these databases should work.