In particular, I don’t think you can make a share-alike requirement on a public domain item.
That’s correct.
“Public domain” is sometimes used in a much vaguer sense to mean the information is out there and being used and shared, but this vaguer sense is best avoided.
I suggest to Epiphany to either:
Strike out “public domain” and replace it the idea of being “open licensed”, or
As Alicorn suggests, declare it public domain. Creative Commons has tools for this (the advantage being that you give a lot more clarity—so I know that you mean the same thing as I understand by public domain). See the nice summary and: Apply CC0 to your own work.
That’s correct.
“Public domain” is sometimes used in a much vaguer sense to mean the information is out there and being used and shared, but this vaguer sense is best avoided.
I suggest to Epiphany to either:
Strike out “public domain” and replace it the idea of being “open licensed”, or
As Alicorn suggests, declare it public domain. Creative Commons has tools for this (the advantage being that you give a lot more clarity—so I know that you mean the same thing as I understand by public domain). See the nice summary and: Apply CC0 to your own work.
Hope that’s helpful.