Ha. I just came here to edit my comment. I remember seeing it before and just checked the docs again. In 5.2 it's STILL considered experiential. Craziness. It took me about an hour to build The basic functionality myself.
Thank you for noticing this, it is not considered experimental anymore. I integrated a change[1] to update the docs; it should percolate through to the site within thirty minutes.
[1]: https://github.com/elastic/elasticsearch/pull/23621