In May of last year, the iterator metamethod (__iter) was implemented (as noted in this post). However, it seems there is nothing yet written in the docs about it. This should be listed with the other metamethods
This should most likely also be mentioned in the for loops documentation.
Thanks for reporting @Neutron_Flow! The improvements came in somewhat piecemeal, with one more minor addition coming in a day or two, but the core pieces are in place and released at this point. Special thanks to metatablecat for all the help over in the open source repository.