Experimenting with `goto-char' and `re-search-backwards' indicates
that this limitation no longer applies. The rewrite using nadvice in
commit
8b62d7427e12bbf07ab3454cc061a6b43ded56dd might have eliminated
this issue.
;; Restrictions:
;; =============
-;; - Traced subrs when called interactively will always show nil as the
-;; value of their arguments.
;; - Only functions/macros/subrs that are called via their function cell will
;; generate trace output, hence, you won't get trace output for:
;; + Subrs called directly from other subrs/C-code