Tests which illustrate how a grammar can be ambiguous, and that this ambiguity can be undetectable. I.e., the test would fail if Daffodil decided that the grammar was ambiguous.

(We are not supposed to check for this situation because it is not portable to do so since it is assumed that many DFDL implementations will NOT be sophisticated enough to even attempt this.... and it actually may be undecidable, not sure,.. and if you use runtime expressions for delimiters, you can't tell until run time anyway, and if those are changing at find granularity - e.g., every record has its own terminator specified,... then you'd be checking while parsing every record which is a bad idea.)

The right thing to do is to NOT check for these ambiguities. It should just make a best effort at runtime, and if the parse is not successful that's ok.