Mike - I am not sure but my gut feeling is that it would start with the most restrictive one first. i.e If empty string ( assuming it has length facet 1) - would match Nothing , then xsd:token which is restricted form of xs:string. I think you are going to get string with white spaces collpsed ( xsd:token) if it not empty string. You can run few tests to see the behavior.. Suman Kalia IBM Canada Lab WMB Toolkit Architect and Development Lead Tel: 905-413-3923 T/L 313-3923 Email: kalia@ca.ibm.com For info on Message broker http://www.ibm.com/developerworks/websphere/zones/businessintegration/wmb.ht... From: Mike Beckerle <mbeckerle.dfdl@gmail.com> To: dfdl-wg@ogf.org, Date: 03/19/2013 12:43 PM Subject: [DFDL-WG] whitespace in DFDL annotations: right now regex is xs:string, expression is xs:token Sent by: dfdl-wg-bounces@ogf.org This came up on the call. The schemas I have for DFDL annotations have DFDLRegularExpression as an xs:string, and DFDLExpression as an xs:token. I have no clue what a union of these types behaves like. But we have a union called DFDLExpressionOrPatternOrNothing which is a 3-way union of DFDLExpression, DFDLRegularExpression, and EmptyString (which is also derived from xs:string but has length facet of 0 as well. -- Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com -- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg