Due to this issue: https://issues.apache.org/jira/browse/DAFFODIL-1975

This is a non-backward-compatible change. The impact of it could be significant 
on existing schemas. Depending on scale of the impact we may have to put in 
flags to turn on/off the changed behavior.  Love to avoid that, but the fixes 
to schemas that are broken by the DAFFODIL-1975 change are subtle - one must 
break up separated sequences into a nest of a few sequences, some separated, 
some not, to preserve current behavior of the schema.

I am inclined to NOT fix this as part of the separator and separator 
suppression work currently in review as PR 


Rather, my plan is to first commit functionality that is compatible with 
current Daffodil behavior, then have separate PRs for individual JIRA tickets 
that change behavior in non-backward-compatible ways like DAFFODIL-1975 does.  
This also helps isolate the tests that verify the change of behavior, which 
also serve as a start at tutorial material for explaining the required changes 
in existing DFDL schemas that use separated sequences.

There are a number of clarifications in discussion on the DFDL Workgroup 
mailing list about behavior of sequences both separated and not, for parsing 
and unparsing. In some cases these, like DAFFODIL-1975, may be backwards 
incompatible. Several of those could be combined into one commit/PR, but in 
general they should be isolated from other changes if non-backward compatible.

Any discussion?

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