The problem with Public Domain is that it does not exist in most jurisdictions. There is no “Public Domain” in (edit: at least parts of) the EU, for example.
In some countries, that might be the case. However, in Germany (where I live), there is no way to have something “not copyrighted”. The author holds the copyright unless explicitly licensed. (Here’s where the CC0 comes in handy, but the CC licenses weren’t made for software…)
The problem with Public Domain is that it does not exist in most jurisdictions. There is no “Public Domain” in (edit: at least parts of) the EU, for example.
What do you mean? Anything that isn’t copyrighted is public domain, including old works.
In some countries, that might be the case. However, in Germany (where I live), there is no way to have something “not copyrighted”. The author holds the copyright unless explicitly licensed. (Here’s where the CC0 comes in handy, but the CC licenses weren’t made for software…)