Sets properties on the message, loaded from an XML MPS file
where the properties to set are located in a
inside the XML config file.
There can be more than one propertySet to "load".
The property values are derived from 3 types of config.
The first config that can return a value as a String to
set onto the message, will be the "value" that is set
as the property.
As it's name suggests, the "value" of this element
will be the value of the JBI property.
This is helpful as a default value, or as a static value.
and
This will obtain the value of an existing property (itself)
or another property on the same message.
This can be helpful when you want the to "ONLY" change the
the value of the property if there is some "xpath" expression
that could not be derived.