This is a trivial example of how to write an external parser; this will replace any page with the word "sex" in it with a warning message (shrug).This should be used with the type set to "File", Mimetype set to "text/html", and Newmime set to "STDIN"
--- SNIP ---
#!/bin/sh
if grep -i sex $1 > /dev/null; then
echo "Content-Type: text/html"
echo ""
echo "<html><head><title>Inappropriate content</title></head>"
echo "<body><font size=6>$HTTP_HOST$HTTP_FILE contains inappropriate content</font></body>"
echo "</html>"
exit 0
fi
# Non-zero exit status returns original content
exit 1
# Alternatively, you can send a Content-type header with the same MIME-type as the original document and cat the file (slower)
echo "Content-type: $SERVER_CONTENT_TYPE"
echo ""
cat $1--- SNIP ---