rfc-3391
The MIME Application/Vnd.pwg-multiplexed Content-Type
The Application/Vnd.pwg-multiplexed content-type, like the
Multipart/Related content-type, provides a mechanism for representing
objects that consist of multiple components. An Application/Vnd.pwg-
multiplexed entity contains a sequence of chunks. Each chunk contains
a MIME message or a part of a MIME message. Each MIME message
represents a component of the compound object, just as a body part of
a Multipart/Related entity represents a component. With a
Multipart/Related entity, a body part and its reference in some other
body part may be separated by many octets. With an
Application/Vnd.pwg-multiplexed entity, a message and its reference
in some other message can be made quite close by chunking the message
containing the reference. For example, if a long message contains
references to images and the producer does not know of the need for
each image until it generates the reference, then
Application/Vnd.pwg-multiplexed allows the consumer to process the
reference to the image and the image before it consumes the entire
long message. This ability is important in printing and scanning
applications. This document defines the Application/Vnd.pwg-
multiplexed content-type. It also provides examples of its use.