Syntax highlighting of doxygen-style markdown in emacs

.emacs

;; After a part is matched, it is no longer modified
;; => put catch-all patterns last
;; https://www.emacswiki.org/emacs/AddKeywords
;; https://www.emacswiki.org/emacs/RegularExpression
;; https://www.gnu.org/software/emacs/manual/html_node/elisp/Faces-for-Font-Lock.html#Faces-for-Font-Lock
(font-lock-add-keywords 'markdown-mode
                        ;; mark each of three groups differently
                        ;; @section label title
                        '(("^\\(@section\\) \\(.+?\\) \\(.+?\\)$"
                           (1 font-lock-constant-face)
                           (2 font-lock-comment-face)
                           (3 font-lock-builtin-face))
                          ;; @ref label                        
                          ("\\(@ref\\)[[:space:]]+?\\(\\_<.+?\\_>\\)"
                           (1 font-lock-constant-face)
                           (2 font-lock-comment-face))
                          ;; `@' not treated as part of symbol but look for next symbol end after `@'
                          ("@.+?\\_>" . font-lock-constant-face)))