+ (let ((invis-spec (make-symbol "notmuch-show-header")))
+ (add-to-invisibility-spec (cons invis-spec t))
+ (overlay-put (make-overlay beg-hidden end)
+ 'invisible invis-spec)
+ (goto-char beg)
+ (forward-line)
+ (let ((header-button (make-button (line-beginning-position) (line-end-position))))
+ (button-put header-button 'invisibility-spec (cons invis-spec t))
+ (button-put header-button 'action 'notmuch-toggle-invisible-action)
+ (button-put header-button 'follow-link t)
+ (button-put header-button 'help-echo
+ "mouse-1, RET: Show headers")
+ ))