Following on from Stephanie's WTX example on last weeks call I think that restricting discriminator to resolving their parents provides the level of control that we need. I have updated Mike's example with this syntax Note I have flattened the schema as I find that easier to read and 'enhanced' some the the dfdl properties. To illustrate the flexibility if 'L' had a test="{ fn:exists( . ) }" discriminator then if an L record had been found then the parse would fail rather than backtracking to Blob. Alan Powell MP 211, IBM UK Labs, Hursley, Winchester, SO21 2JN, England Notes Id: Alan Powell/UK/IBM email: alan_powell@uk.ibm.com Tel: +44 (0)1962 815073 Fax: +44 (0)1962 816898 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