Bradley M. Kuhn:
> Could you explain a bit further why the extra parenthesis grouping is
> needed when only ORs are involved?
As you guessed, the parentheses are not *needed*. The SPDX spec says that
parentheses SHOULD be used when there are multiple license identifiers or
license refs, but this is a SHOULD not a MUST.
The section you want to consult is SPDX specification version 2.1, Appendix IV
("SPDX License Expressions"):
https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60
Subsection "Composite License Expressions" says:
"More expressive composite license expressions can be constructed using "OR",
"AND", and "WITH" operators similar to constructing mathematical expressions
using arithmetic operators. For the Tag:value format, any license expression
that consists of more than one license identifier and/or LicenseRef, should be
encapsulated by parentheses: "( )". This has been specified to facilitate
expression parsing. Nested parentheses can also be used to specify an order of
precedence which is discussed in more detail in subsection (4)."
So the spec recommends using parentheses when there are multiple license
identifiers. Again, this is only a SHOULD, not a MUST. I view this as a
stylistic recommendation.
--- David A. Wheeler
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