Minor changes in json.el

* lisp/json.el (json-advance): Simpler docstring.
(json-read-escaped-char): Use xdigit subform in rx expression.
(json-read-string): Just use = for char comparison.

lisp/json.el

@@ -188,7 +188,7 @@ Unlike `reverse', this keeps the property-value pairs intact."
 ;; Reader utilities
 
 (defsubst json-advance (&optional n)
-  "Skip past the following N characters."
+  "Advance N characters forward."
   (forward-char n))
 
 (defsubst json-peek ()
@@ -381,13 +381,13 @@ representation will be parsed correctly."
      ;; this clause overlaps with the next one and therefore has to
      ;; come first.
      ((looking-at
-       (rx (group (any "Dd") (any "89ABab") (= 2 (any "0-9A-Fa-f")))
-           "\\u" (group (any "Dd") (any "C-Fc-f") (= 2 (any "0-9A-Fa-f")))))
+       (rx (group (any "Dd") (any "89ABab") (= 2 (any xdigit)))
+           "\\u" (group (any "Dd") (any "C-Fc-f") (= 2 (any xdigit)))))
       (json-advance 10)
       (json--decode-utf-16-surrogates
        (string-to-number (match-string 1) 16)
        (string-to-number (match-string 2) 16)))
-     ((looking-at "[0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f]")
+     ((looking-at (rx (= 4 xdigit)))
       (let ((hex (match-string 0)))
         (json-advance 4)
         (string-to-number hex 16)))
@@ -396,14 +396,14 @@ representation will be parsed correctly."
 
 (defun json-read-string ()
   "Read the JSON string at point."
-  (unless (char-equal (json-peek) ?\")
+  (unless (= (json-peek) ?\")
     (signal 'json-string-format (list "doesn't start with `\"'!")))
   ;; Skip over the '"'
   (json-advance)
   (let ((characters '())
         (char (json-peek)))
-    (while (not (char-equal char ?\"))
-      (push (if (char-equal char ?\\)
+    (while (not (= char ?\"))
+      (push (if (= char ?\\)
                 (json-read-escaped-char)
               (json-pop))
             characters)