Mike, More correctly, you mean Step[Index]/Step[Index]/Step[Index], but that's fine as that is handled by the definition of AxisStep as it includes Predicate. However removing FilterExpr entirely removes PrimaryExpr and all it brings with it, like literals and function calls and the use of "." so your change on its own simplifies things too much. What I think you would need is: StepExpr ::= FilterExpr | AxisStep PathExpr ::= (("/" RelativePathExpr?) | RelativePathExpr) | FilterExpr I can see (at least) one problem with only allowing FilterExpr to appear on its own, namely that you lose the ability to use "." in conjunction with a path, so even the above is not sufficient. Looking at what we have done in the original spec, all we did was edit the BNF to remove things we didn't support, making what resulted easily comparable to standard XPath 2.0. The resultant BNF implies several things that we do not support in DFDL, so we qualified the BNF with some notes. For example, DFDL only allows the use of Predicates to index arrays, so there is a note saying that a Predicate must result in an integer else it's an SDE. I think we should do the same for errata 2.101 - leave the BNF alone and add a new note to the list. And beef up the words at the start of section 23.4 to make it clear how the BNF should be read. Also noticed that the BNF in the spec is not stand-alone as the constructs for StringLiteral etc are not reproduced, and rely on the reader reading XPath 2.0 spec. Regards Steve Hanson Architect, Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh@uk.ibm.com tel:+44-1962-815848 From: Mike Beckerle <mbeckerle.dfdl@gmail.com> To: dfdl-wg@ogf.org, Date: 05/02/2013 23:08 Subject: [DFDL-WG] what do we allow in DFDL expressions after "/" Sent by: dfdl-wg-bounces@ogf.org In reexamining the grammar for the DFDL expression language, I have the following question In a path Step/Step/Step[Index] What can Step be? I know it can be ".." or parent::QName or child::QName or just an NCName or QName, Those are all what the XPath grammar calls AxisStep. anything else? The grammar can be changed in a very small way from the original XPath grammar if the above are the only possibilities. the clause StepExpr ::= FilterExpr | AxisStep can just be changed to StepExpr ::= AxisStep -- 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 Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU