Here is the description of the virtual path format:

The canonical form
==================

   [basepath]#handler[options][:parameters][/internalpath]

'basepath', if given is an ordinary file path (can be a regular file,
or a directory, and can be a real or a virtual path).

'#' is the character that prefixes the handler name and is
defined by VDEV_SEP_CHAR. 

'handler' is the name of the file handler (filter, remote file
access or other processing unit). Handler names consist of only
alphanumeric characters ([a-z0-9_]). Handler names are case
sensitive, and should always be lower case.

'options' is an optional field containing "mount options". These
options should not change the content of the virtual mount, only the
permissions or mode of access. For example:

'+' - read-write
'=' - don't cache

'parameters' are part of the path, but before the mount root. 

'internalpath' is the optional path within the handlers file
structure. It is prefixed by '/'.

Notes: 

   The only special characters are '#' and '/'.

   If an ordinary (non virtual) file name contains a '#', then this
   file can be accessed normaly (i.e. existing files take
   precedence over virtual ones). If a virtual path contains '#'
   (even in the real path part) they must be represented by '##'.

   (This way a situation can arrise, where you can't access a
   virtual file, because a real file 'shadows' it. This is a case
   of tough luck ;)

Examples (not all of these are implemented yet): 

   /home/user/archive.tar.gz#ugz#utar/path/file
   /#ftp:host.dom.org/pub/README
   /#http:www.dom.org|some|where|index.html
   /#http:localhost:8000|~user|file 
   file#gz-9
   /#floppy:a/xyz
   
The non-canonical virtual paths
===============================

This is to make life easier for the user.

   dir/file.ext#[/extrapath]

With this notation, the '#' is substituted with the handler(s)
determined from the file's extension. Any parameters after the # are
passed to the last expanded handler.

Examples:
   file.gz#             == file.gz#ugz
   archive.tar.gz#/dir  == archive.tar.gz#ugz#utar/dir
   archive.tar.gz#+/dir == archive.tar.gz#ugz#utar+/dir	
