Re: Please document the caching and its user options

[Daniel Clemente]

> > 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.)
> Hmm. What aspect of caching do you want us to document?
> FYI, Org mode has been doing various forms of caching since
> forever. Recently, we just employed a bit more regular API and
> introduced one more kind of caching - parser cache. In addition to the
> previously existing image cache, publishing cache, ID cache, clock
> cache, etc.

One of the discussion points is specifically org-persist, which is
what creates files on disk.
There have been reports, like
https://lists.gnu.org/archive/html/emacs-devel/2024-06/msg00203.html,
or Eli's message here, mentioning that ~/.cache/org-persist is created
when the user doesn't want it or expect it.

In particular, when setting (setq org-element-cache-persistent nil)
org-mode *should not* create an org-persist directory anywhere. And I
think it shouldn't activate org-persist timers (it does now) or hooks.
The user's preference should be respected.

That's a code change.
If you just want to update documentation, a starting point can be
org-element-cache-persistent's documentation, which is just "Non-nil
when cache should persist between Emacs sessions.", and doesn't
mention that some files will always be created even if it's nil. It
also doesn't explicitly mention that it will create files (better be
explicit about this), or where (or how to control where), or which
content (i.e. just statistics, or parts of possible private org
files).

I suggest making an explicit difference between "caching in memory"
and "caching by storing files on disk".
For instance:
(defvar org-element-use-cache t
  "Non-nil when Org parser should cache its results.")
>From that description, it's not clear to a new user whether they're
creating files on disk (as caches often do) or not.