Update

public_domain.md

@@ -56,6 +56,7 @@ For an example of a project project properly released into public domain see the
 
 There are quite a few places on the Internet where you may find public domain works. But firstly let there be a warning: you always **have to** check the public domain status of works you find, it is extremely common for people on the Internet to not know what public domain is or how it works so you will find many *false positives* that are called public domain but are, in fact, not. This article should have given you a basic how-to on how to recognize and check public domain works. With this said, here is a list of some places to search (of course, this list will rot with time):
 
+- Very **old works and traditional folk art** are mostly in the public domain, e.g. Shakespeare's plays or folk songs. Nice example of reusing folk art is e.g. [Richard Stallman's](rms.md) *Free Software Song* that takes the melody of a Bulgarian folk song *Sadi Moma*. However watch out for traps, e.g. [trademarks](trademark.md) that may exist despite no copyright (e.g. Encyclopedia Britannica) or weird nationalist laws against disrespecting a country's folklore that may possibly exist too.
 - **[Wikimedia Commons](https://commons.wikimedia.org/wiki/Main_Page)**: Contains only free as in freedom works among which are many PD ones. You can search for them with queries such as `cat incategory:cc-zero`. This site is quite reliable and serious about licensing, if you find a work marked as PD here, you can be reasonably sure this information is true.
 - **[Internet Archive](https://archive.org/)**: The biggest Internet archive, huge amount of mainly old works such as scanned books and photos. Beware that this site contains all kinds of works from PD to [proprietary](proprietary.md) and works marked as PD should be checked as there can be errors. There is an *advanced search* tool that can help in searching for PD works, for example [this query](https://archive.org/search.php?query=possible-copyright-status%3A%28NOT_IN_COPYRIGHT%29%20OR%20licenseurl%3A%28%22http%3A%2F%2Fcreativecommons.org%2Fpublicdomain%2Fmark%2F1.0%2F%22%29%20OR%20licenseurl%3A%28%22http%3A%2F%2Fcreativecommons.org%2Fpublicdomain%2Fzero%2F1.0%2F%22%29) tries to achieve this.
 - **[Opengameart](https://opengameart.org/)**: Site for sharing free as in freedom [game](game.md) art (pictures, 3D models, sounds, ...) among which are many under [CC0](cc0.md), i.e. PD. Submitted works are checked reasonably well so any CC0 work you find here is likely truly PD.