Apparently, some lawyers have raised issues with the public domain ”dedication” or ”certification” as it was worded. Indeed, the logic behind the dedication was US copyright law, which does not recognize inalienable moral components of copyright. The new ”zero copyright” makes it clear that the dedication is only valid ”to the extent allowable by [copyright] law” and that any other rights such as patents or personality rights are not affected. Ok, legally perhaps more clear but I don’t know if there is really any difference in practice. CC0 is essentially public domain in other words.