Where is the rest of the MySQL "HANDLER" documentation?

Question

I've been a long time user of Handlersocket for MySQL / Percona, but other than MariaDB keeping it going, it's been dead for a long time now. The final nail in the coffin seemed to be MySQL choosing to go with Memcached.

So that in mind, I was looking at all of my alternatives, and in all the noise out there relating to Handlersocket, I had missed the existence of MySQL's HANDLER capability which, other than the separate socket access, provides very similar features to HS.

The problem is, handler is such a ubiquitous term that I'm getting far too much static looking for documentation or examples. The only page I've been able to locate was the original man page at https://dev.mysql.com/doc/refman/8.0/en/handler.html. I've run across answers that skirt it like https://dba.stackexchange.com/a/4589/23271, but there doesn't seem to be anything more on this feature.

I have questions like:

• There is a HANDLER .... READ .... request type, but is there a HANDLER .... WRITE .... capability?

• Is there a way to restrict the response to a specific selection of the table fields? There was in handlersocket, but I don't see any reference to it on the man page.

• What other capabilities or features does HANDLER have?

If you can answer any of the above, I'd be grateful, or if you have links to any further resources, I'm happy to read up on my own. Thanks!