"The copyright or patent on the work has expired." The actual formula is max(1923, year of first publication + 96) in the U.S. and year of death + 71 in the E.U.
<li>
was designed to handle.
"The author or inventor explicitly disclaims any proprietary interest." Not necessarily. Some law experts believe that it's impossible for an author to put a copyrightable work into PD. (Anyone have a source for this?) Even then, it's still a really Bad Idea for an author to release a work into PD, as it fails to disclaim implied warranty and opens the author up to liability. Better to release it under a simple permissive license similar to the new BSD license.
And the soft line breaks after sentences serve a purpose: they make the diffs much cleaner. --Damian Yerrick
Can we have an example other than Mark Twain?: one story of his wasn't published in his lifetime, and finally appeared in 2001, so it's still in copyright. --Vicki Rosenzweig