Emacs: Replace Invisible Unicode Chars 🚀

By Xah Lee. Date: 2015-10-12. Last updated: 2023-11-23.
Here's a command that replaces invisible characters.
They happen often when copying text from Twitter etc sites.
(defvar xah-replace-invisible-char-list nil
"A alist used by `xah-replace-invisible-char'.
Each element is (codepoint . nameString).
The codepoint is an integer.
The nameString is for documentation purposes.
")

(setq
 xah-replace-invisible-char-list
 '((65279 . "ZERO WIDTH NO-BREAK SPACE")
   (8203 . "ZERO WIDTH SPACE")
   (8207 . "RIGHT-TO-LEFT MARK")
   (8238 . "RIGHT-TO-LEFT OVERRIDE")
   (8206 . "LEFT-TO-RIGHT MARK")
   (65532 . "OBJECT REPLACEMENT CHARACTER")
   (65024 . "VARIATION SELECTOR-1")
   (65025 . "VARIATION SELECTOR-2")
   (65026 . "VARIATION SELECTOR-3")
   (65027 . "VARIATION SELECTOR-4")
   (65028 . "VARIATION SELECTOR-5")
   (65029 . "VARIATION SELECTOR-6")
   (65030 . "VARIATION SELECTOR-7")
   (65031 . "VARIATION SELECTOR-8")
   (65032 . "VARIATION SELECTOR-9")
   (65033 . "VARIATION SELECTOR-10")
   (65034 . "VARIATION SELECTOR-11")
   (65035 . "VARIATION SELECTOR-12")
   (65036 . "VARIATION SELECTOR-13")
   (65037 . "VARIATION SELECTOR-14")
   (65038 . "VARIATION SELECTOR-15")
   (65039 . "VARIATION SELECTOR-16")))

;; "\ufeff\\|\u200b\\|\u200f\\|\u202e\\|\u200e\\|\ufffc\\|\ufe0f"

(defun xah-replace-invisible-char ()
  "Query replace some invisible Unicode chars.
The chars replaced are from `xah-replace-invisible-char-list'.

Search begins at cursor position. (respects `narrow-to-region')

When the command is done, call `exchange-point-and-mark' to go back to the original cursor position.

URL `http://xahlee.info/emacs/emacs/elisp_unicode_replace_invisible_chars.html'
Version: 2018-09-07 2023-06-22 2023-07-12"
  (interactive)
  (let ((case-replace nil)
        (case-fold-search nil)
        (xregex
         (regexp-opt
          (mapcar (lambda (x) (char-to-string (car x))) xah-replace-invisible-char-list))))
    (push-mark)
    (while (re-search-forward xregex nil t)
      (let (xcharId xname)
        (setq xcharId (string-to-char (match-string 0)))
        (setq xname (get-char-code-property xcharId 'name))
        (if (y-or-n-p
             (format "found 「%s」 codepoint 「%s」, replace?" xname xcharId))
            (replace-match "")
          nil
          ))))
  (print "Done replace invisible chars or none."))