Please use CC0[0], not "public domain".

Several countries (esp. in Europe) do not recognize the concept of the public domain (and/or limit an individual's right to place their content in the public domain "prematurely")[1]. In these countries, declaring your code to be in the public domain does nothing, whereas using a CC0 license is a more legally defensible way of achieving the same goal (allowing others to use your work freely without fear that you could later revoke that right).

[0] https://creativecommons.org/publicdomain/zero/1.0/

[1] https://en.wikipedia.org/wiki/Public_domain#Dedicating_works...