property that uses relative indexes, UIDs property will
return reference to some user based on his unique ID - unique value
he got when he connected. ID for the user will not be
changed during client's connection, and no two users
will have the same ID as long as the server is started.
You can freely store user's ID in your program and
access the reference to the user later on, from any
function - of course, assuming the client doesn't
disconnect in the meantime.