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.
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.
Edit: As a note, I did find out how it worked by doing source code diving two months ago.