Please document the caching and its user options

[Eli Zaretskii <eliz@gnu.org>]

I needed to visit org.org, the Org manual, today, and to my surprise
saw Emacs writing some data files into the ~/.cache/org-persist/
directory.  What's more, Emacs popped a buffer out of the blue telling
me that it could not safely encode the data written to (I presume)
some of those files, and asked me to select a safe coding-system.

By randomly poking here and there, I've succeeded to figure out that
this is due to org-element's caching of data from parsing Org files.
It seems this caching is turned on by default, but is not documented
in the Org manual, and in particular there's nothing in the manual
about turning off the caching.

Please document the caching features of Org in the manual, including
how to turn that off.  (I also question the wisdom of turning this on
by default without as much as a single request for confirmation from
the user.)

Please also make sure that the code which actually writes the data to
the cache files makes a point of binding coding-system-for-write to a
proper value (probably utf-8-unix), or forces
buffer-file-coding-system of the buffer from which it writes to have
such a safe value, to avoid annoying and unexpected prompting of the
user to select a proper encoding.  Lisp programs that write files in
the background cannot fail to set a proper encoding, because the call
to select-safe-coding-system is not supposed to be triggered by Lisp
programs unless they run as a direct result of a user-invoked command.

I've seen those problems in Emacs 29.3.  If these issues are already
solved in what will become Emacs 30, then my apologies, and kudos to
whoever solved them.  (However, the latest Org manual still keeps
completely silent about these features and their control by users.)

Thanks.