After my last note on identifiers, Leo Talirz pointed me to a great riff ¹ on Tim Berners-Lee’s classic note ² on “cool URIs”. In the “Cool DOIs” article, Fenner breaks down a DOI into three parts: proxy, prefix, and suffix. A proxy is a server that maintains a map from prefixes to registrants. Example proxies are https://doi.org/ and https://hdl.handle.net/. An example prefix is 10.5281.