The IRS is a US federal agency, though. They can claim no copyright on the code. It should be be public domain.

Unless it was written by a contractor who then gave the copyright to the IRS. This is a very common situation. The federal government is not barred from having copyrights.

That would be a fun legal rabbit hole to descend into.

I don't know about fun, but it would definitely be expensive.

"Fun" from a research perspective. (I've got friends who are IP lawyers and enjoy talking about this stuff.)

FOIA results can definitely go into public domain. That's sort of the point.

> That's sort of the point.

It really isn't - the point is freedom access, not free use. Information acquired this way doesn't magically become public domain, it may (or may not) have other constraints on it.

See e.g. https://www.justice.gov/oip/blog/foia-update-oip-guidance-co...