The MessageId property returns a numeric identifier for the
most recent prompt and response. If the control is not connected to a
provider, or a prompt has not been sent, this property will return
zero.
Message identifiers are session-specific and are guaranteed to be
unique only within the client session in which they were created.
Applications must not rely on the internal assignment strategy used to
generate these identifiers. The only guaranteed behavior is that newer
messages will always receive larger identifier values than older
messages.
The GetMessage method can be used to retrieve the prompt and
response for a specific message.