nsIMultiPartChannel in Firefox 2.0

 readonly attribute to access the underlying channel

 Access to the Content-Disposition header field of this part of
 a multipart message.  This allows getting the preferred
 handling method, preferred filename, etc.  See RFC 2183.

 Set to true when onStopRequest is received from the base channel.
 The listener can check this from its onStopRequest to determine
 whether more data can be expected.

 Attribute guaranteed to be different for different parts of
 the same multipart document.