- support the TraX interface, so that Xalan2 and Saxon 6.1(?) work
from the same Java class

- support for cached stylesheets

- allow for externally specified stylesheets. Define menu entries for
them that can be customized to appear as children of other menus than
the top level.

- allow starting an external program (possibly using metamail) based
on the media type specified in the stylesheet and on an association
(customizable in Emacs) between media types and MIME types. How to do
the same on Windows?

- automagically recognize the type of the result in the output buffer
and apply the right mode to it. Should this be based on the MIME type?