The DFDL expression language supports the string(...) function in the xs (xml schema) namespace, not the fn (xpath functions) namespace. A few places in the spec use fn:string(...). These need to change to xs:string(...) I've added this to issue https://redmine.ogf.org/issues/233 which is the one of typographical errors. 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>