Can OSI specify that public domain is open source?

[Karl Fogel]

I'd like to work some material onto our web site confirming that
software in the public domain (in the copyright-related sense used in
the United States, which we would make clear) is open source.

Yes, I realize that we talk about "licenses" everywhere, and the text
would make clear that public domain is not really a license, etc, etc.
But I've seen this point cause confusion on a number of lists now,
including some that matter, and we should just put it to bed.

I'm happy to do the work; I just want to make sure there isn't some
historical debate I'm stepping into here.  Please let me know.  Silence,
after a reasonable period of time, will be assent :-).

Best,
-Karl