[DFDL-WG] How to parse an email address

Suppose I want to model an email address: dfdl-wg@ogf.org It's a sequence of a string, an a character (@), and a string. In the MBTK it might look like this: [cid:image001.png@01CE10EC.6600AE50] The problem, of course, is that the parser will grab all of "dfdl-wg@ogf.org" instead of just "dfdl-wg". Setting validation facets doesn't help, b/c validation happens after parsing. Setting @ as a separator or terminator would work, but that doesn't seem right either, as the @ is part of the email address, and I would want to keep it in the infoset. How do I think about this problem? TIA