Some elements depend on the value of an OVC, and so we cannot wait until the end of unparser to evaluate them.
DFDL-1342 Unparse - AlignmentFill not yet implemented
DFDL-1507 Implement outputValueCalc for elements where length depends on value (alignment related)
DFDL-1561 RoundTrip: PCAP examples do not round trip
DFDL-1566 TestParseUnparseMode fails to roundtrip or unparse