;; 2023-06-25
;; each tag must have a opening tag and a closing tag.
;; except if the tag ends in /> then it is a self closing. in xml.

;; tag sequence occure in 2 ways
;; one is nested, like so
;; ( ( 3c9de ( 530 ) toh ) )
;; the other situation is sequential
;; ( ) () ()

;; algorithm outline
;; one way, is to grab whole file, split into a list by angle braket, then process each item.

;; second way, is open the file, then move cursor to beginning, then, search for the next occurance of angle bracket. then, grab it, it is a tag, may be opening tag or closing, push it onto stack.
;; continue.

(defun xah-validate-xml-buffer ()
  "validator for xml, check well-formedness
version 2023-06-25"
  (interactive)
  (let (xp1 xp2 xtag
            (xstack '()))
    ;; get current pos, find next angle brack pos, grab text in between, that's one tag, push it to stack
    (goto-char (point-min))

    (while (re-search-forward "[<>]" nil t)
      (progn
        (if (eq (char-before) ?<)
            (setq xp1 (1- (point)))
          (error "error found at position %s" (point)))
        (re-search-forward "[<>]" nil t)
        (if (eq (char-before) ?>)
            (setq xp2 (point))
          (error "error found at position %s" (point)))
        (setq xtag (buffer-substring-no-properties xp1 xp2))

        (if (xah-is-selfclosing xtag)
            nil
          (push xtag xstack)))

      ;; xah-html--opening-tag-p

      ;; some code to check stack
      ;;
      )

    (print xstack)))

(defun xah-is-selfclosing (Tagstring)
  "return t if Tagstring ends in />"
  (if (string-equal "/>" (substring Tagstring -2))
      t
    nil
    ))