Emacs html-mode for .zpt and .dtml

I've been using XEmacs on windows a lot lately to edit .zpt and .dtml files (template files for Zope) and to get automatic html-mode on these files you need this in your .emacs or 'custom.el':

(add-to-list 'auto-mode-alist '("\\.zpt$" . html-mode))
(add-to-list 'auto-mode-alist '("\\.dtml$" . html-mode))

This is not the first time I've had to add this. Better write it down so I've got it documented somewhere.