Each client connection that is accepted by the server is assigned
a unique numeric value. This value is by the application to
identify that client session, and is different than the socket handle
allocated for the client. Client IDs are unique
throughout the life of the server session and are never
duplicated.
This property only returns a meaningful value when accessed from
within an event handler, or a function that has been called from
within an event handler. This property will always return a value of
zero when accessed outside of an event handler.