Finally, here's a draft document about outputValueCalc, unparsing, and, variables, and such. Also attached is a zipped eclipse project containing two subdirs: outputValueCalc has examples of ... outputValueCalc, and variables has an envelope payload example enhanced and corrected somewhat over a prior one I sent. There's one entirely new concept here. I added an attribute to dfdl:defineVariable to specify whether the variable is for input (parsing) or output (unparsing). I was unable to get things to work in any simple manner without separating the two classes of variable. This doesn't seem too bad actually. ...mike Note: Please do not send sensitive data in unencrypted form in email. We cannot provide secure transit for email over the Internet. Mike Beckerle | CTO | Oco, Inc Tel: 781-810-2125 | 100 Fifth Ave, 4th Floor, Waltham, MA 02451 | mbeckerle@oco-inc.com | www.oco-inc.com <http://www.oco-inc.com/> Blog: cboblog.typepad.com <http://cboblog.typepad.com/> TURNING DATA INTO ANSWERS. FASTER THAN YOU EVER IMAGINED.