I ran into an interesting format today called RINEX that is problematic for DFDL v1.0: http://acc.igs.org/misc/rinex304.pdf This format has a multi-line header with various kinds of header lines which are 80 characters, but characters 1 to 60 are data, and 61 to 80 are the "label", and you need the label in order to know how to parse the data of each header line. This either requires deep (and slow) speculation, or some sort of look ahead feature. E.g., See page 69 of that spec document for an example. The headers appear not only at the start of the file, but at the start of each data block. We have run into the need for short, fixed-distance look ahead before in other formats. In the case of RINEX the lookahead is exactly 60 characters. In other formats it is also a very short distance, but one which is tricky to figure out as the spec doesn't say exactly how big the region to be looked past is. One would have to figure it out from the data format spec. It's always a constant of course. Mike Beckerle Apache Daffodil PMC | daffodil.apache.org OGF DFDL Workgroup Co-Chair | www.ogf.org/ogf/doku.php/standards/dfdl/dfdl Owl Cyber Defense | www.owlcyberdefense.com