None numeric exclusion constraints using GIST

Is there provision for creating none numeric exclusion constraints on
GIST indexes?

From my reading of the following, ti doesn't appear to be possible:

http://www.postgresql.org/docs/9.1/static/sql-createtable.html#SQL-CREATETABLE-EXCLUDE
http://www.postgresql.org/docs/9.1/static/datatype-geometric.html
http://www.postgresql.org/docs/9.1/static/sql-createindex.html
http://www.depesz.com/index.php/2010/01/03/waiting-for-8-5-exclusion-constraints/


Is this correct?

--
Regards,
Richard Broersma Jr.