Hey, I echo to #664 and the discussions on the ABNF grammar described as part of SPDX v3.0.

Given RFC 5234 Section 2.3 "Terminal Values":

ABNF strings are case insensitive [...]

This imply that "TEST" could produce "test", "tEsT", "TEST", and so on.
As this was not clear for most of the reviewers and later on the users of the RFC, the IETF published RFC 7405.

Nevertheless, the current ABNF grammar contains the alternation group ( "WITH" / "with" ) that produces the same results.
I suggest this alternation group is either removed to enhance readability OR replaced by ( %s"WITH" / %s"with" ) as in my understanding it better fits the idea of rule compound-expression.
The same goes on for AND and OR.

Moreover, this should also be clarified for "DocumentRef-", "LicenseRef-" and "AdditionRef-" which should be prefixed by %s.