How to get the character corresponding to syntax in a major-mode

How can I get the character (or set thereof) corresponding to a given syntax character in a major-mode?

For example, I want to be able to get the escape character, eg '\' in most modes like elisp or C. I can't find a function that would return the character(s) corresponding to a syntax class -- in this case the escape syntax class, ie. (string-to-syntax "\\") ;; => (9) in Lisp/C modes.

So, how can I go the other way, eg. (some-function '(9) major-mode) ;; => "\\"

Syntax tables are char-tables, you can use map-char-table to check every rule in the syntax talbe, for example,

(defun foo (syntax-code syntax-table)
  "Return chars (or char range) with SYNTAX-CODE in SYNTAX-TABLE."
  (let (result)
    (map-char-table
     (lambda (k v)
       ;; k is either a char or (FROM . TO)
       ;; v is (SYNTAX-CODE . MATCHING-CHAR)
       (when (= (car v) syntax-code)
         (push (pcase k
                 (`(,from . ,to) (list (string from) (string to)))
                 (_ (string k)))
               result)))
     syntax-table)
    (nreverse result)))

(foo 9 emacs-lisp-mode-syntax-table)
;; => ("\\")