External packages (e.g., a couple that I've written) may wish to
provide navigation commands that automatically reveal previews and
folds, but auto-reveal behavior is currently controlled by defcustoms,
such as preview-auto-reveal, that are not easily extended:

(defcustom preview-auto-reveal
  '(eval (preview-arrived-via (key-binding [left]) (key-binding [right])
                              #'backward-char #'forward-char))
  "...")

I attach a patch that addresses this, without affecting default
behavior, by changing the default value of preview-auto-reveal so that
it refers to a list, (defcustom preview-auto-reveal-commands).
Similarly for TeX-fold-auto-reveal.

Thanks, best,

Paul