(defun normalize (c)
  (case c
    ((?0) ?₀)
    ((?1) ?₁)
    (t c)))

(auto-overlay-load-definition
 'short-id-subscripts11
 `(word :id 'x0
        ((,(rx "x" (group-n 1 num)) . 1)
         ;; (display . "₀")
         (display . (lambda ()
                      (normalize (following-char))
                      "*")))))