I'm not a fan of the whole WHATWG spec/process, but it has datalist and other not-so-well-known elements covered. If you prefer a succinct reference (rather than the full browser-melting spec), there are other other sources than WHATWG's spec or MDN helping with discoverability, such as mine (as a proper SGML DTD grammar, no less) [1].

[1]: <http://sgmljs.net/docs/w3c-html52-dtd.html>