(defun register-yank-media-handler (types handler)
"Register HANDLER for dealing with `yank-media' actions for TYPES.
TYPES should be a MIME media type symbol, a regexp, or a list
-that can contain both symbols and regexps."
+that can contain both symbols and regexps.
+
+HANDLER is a function that will be called with two arguments: The
+MIME type (a symbol on the form `image/png') and the selection
+data (a string)."
(make-local-variable 'yank-media--registered-handlers)
(dolist (type (ensure-list types))
(setf (alist-get type yank-media--registered-handlers nil nil #'equal)