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Note: changing the code to support pattern is delimiter would not be that much work so time to implement should not be a consideration.
I have made the necessary local changes to reverse the logic to make it a search by regex delimiter and still find the AO000, AO001, AO002, AO003, AO004, AV000, AV001 and AV002 tests are still failing due to an inability of the parser to find the initiator property.
And I reverted back to the original implementation and test thanks to Mike's comment below; we will treat lengthKind="pattern" as a regex match against the field. What has yet to be decided is how to handle field delimiters and separators.
MikeB said: Best to go to the current draft of the DFDL spec. The AA-BG tests were part of the original daffodil code base, and that was developed based on a very early draft of the DFDL standard, which has since changed a great deal as it has converged toward an agreed standard. In particular, way back somebody suggested "why not let delimiters be regular expressions?" For a while this was entertained, and that's when the original daffodil code base was created along with tests AA-BG. But this was later viewed as too much generality (hence complexity, especially when debugging "why doesn't my DFDL schema work???"), for not enough benefit.
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