The MakeConnection element is sent in the body of a one-way message that
establishes a contextualized back-channel for the transmission of messages
according to matching criteria (defined below).
The MakeConnection policy assertion indicates that the MakeConnection protocol
(operation and the use of the MakeConnection URI template in EndpointReferences)
is required for messages sent from this endpoint.
When MakeConnection is used, and a message is returned on the
transport-specific back-channel, the MessagePending header
SHOULD be included on the returned message as an indicator
whether there are additional messages waiting to be retrieved
using the same selection criteria that was specified in the
MakeConnection element.