An expression evaluating to an object
of type XMPPMessage.
value
A String value.
Remarks
A Custom Field. You can assign any string value here.
This property can be useful if, i.e. you want to
differentiate messages received from the same person. This
value is exchanged with the peer when message is sent.
Usually when person replies it will put same value in
Thread property to the message that is coming back.