(defun nxmlm-hook()

  (custom-set-faces
   ;; Get rid of that goddamn underline face
   '(rng-error-face ((t (:foreground "yellow" :weight light)))))

  ;; Start flyspell, checking only prog-mode faces.
  (flyspell-prog-mode)

  ;; And add normal xml text to that list of prog-mode faces.
  (add-to-list 'flyspell-prog-text-faces 'nxml-text-face)
  )

(add-hook 'nxml-mode-hook (function nxmlm-hook))