Stuff the [[plugins/attachment]] plugin is currently missing, that might be
nice to add:

* `mimetype()` pagespecs. (Using a mime type sniffer.)
* Virus scanning.
* Add a progress bar for attachment uploads (needs AJAX stuff..)
* Maybe optimise the "Insert Links" button with javascript, so, if
  javascript is available, the link is inserted at the current cursor
  position in the page edit form, without actually reposting the form.
  (Falling back to the current reposting of the form if javascript is not
  available of course.)
* Set `$CGI::POST_MAX` to some sane value (ie, larger than the largest
  configured `maxsize()` in the pagespec, or if none is configured,
  something reasonable. Just as a belt-and-suspenders DOS prevention.
* Only allow attachments to be added to a given list of pages.
  Maybe a pagespec like `parent(patches/*)`