Preview can be used to view content before it's sent to the browser.
Content can be accepted or rejected.  Image content such as image/gif
and image/jpeg is displayed in a pop-up window.  Text (HTML) content
is displayed in a text window which allows the text to be modified
before it's sent to the browser.  This can be very useful to edit HTML
on-the-fly.

This filter has the following configurable preferences:

* Preview.contentTypes

  List of content types to preview.  Partial content types can
  be specified.  "text" will match "text/plain" and "text/html".
