At the least, I cannot find any mention of the specifics anywhere on the main GitHub page - this is the best that I can tell: http://facebook.github.io/react/docs/top-level-api.html#reac... . I do know the recommendation is to use JSX, and I can see why, but more visibility of the API would be better.
Edit: As a note, I did find out how it worked by doing source code diving two months ago.
Re:Angular 2 Core
by purpletoned on Saturday October 25, 2014 @03:33PM
(#8509122)
I think there's a page or two that describes what the jsx transformer does(which is it converts them to React.DOM elements IIRC). I think that's where I learnt that you could use raw JS functions instead of jsx, even though it said that jsx should be preferred or something to that effect.
React.DOM.div(), etc. are part of React's public API -- if we didn't document them, that's a mistake.