Feel free to create a pull request. In this case, I think there will
be little resistance to aligning the specification with the schema on
this point (and the schema usually takes precedence over the
specification anyway in case of discrepancies).
Your pull request might sit for a while until I have had some time to
document and implement our plans for a better development process for
CSL. It’s rather trivial to accept the change, but I want to make sure
that the stakeholders are at least aware of the change before I merge
it (will inform the mailing list) and that it ends up in the changelog
for the next release. I’m focused on moving the CSL website from
WordPress to GitHub pages right now, but that should be done in the
next few weeks.