W. Trevor King [mailto:wking@...]:

The Appendix V wording for that is:

Representing Multiple Licenses

Multiple licenses can be represented using a SPDX license expression
as defined in Appendix IV. A set of licenses must be enclosed in
parentheses (this is a convention for SPDX expressions).

which is a strange combination of “must” and “convention”. But it sounded
to me like a requirement for parens around the whole license expression,
and not a suggestion for additional parens within the license expression. In
[2], I tried to express that with the ‘enclosed-license-expression’ rule [3]
and its explanatory paragraph [4].

Appendix V only applies to license expressions within files, not license expressions generally.
If we interpret "must" as a real requirement, then within files you must use (...) in these cases.
In contrast, Appendix IV applies in all cases.

I think the Appendix V additional requirement should be dropped, frankly.
That is, I think we should remove the statement, "A set of licenses must be enclosed in
parentheses (this is a convention for SPDX expressions)."
I'm fine with a style recommendation as a "should" in appendix IV, which is already there. But if someone forgets the parentheses, the license expression should still be accepted because it's unambiguous and has been historically allowed by the specification.

--- David A. Wheeler