The spec for property dfdl:choiceDispatchKey says "The expression must evaluate to an xs:string which must not be the empty string." It fails to say whether this "must not" is a processing error or schema-definition error. Consistent with delimiter expressions evaluating to empty string, I believe this should be an SDE. ...mikeb Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy <http://www.ogf.org/About/abt_policies.php>