Creates an object that waits for a set of messages to arrive.
| Parameters | accept | message name or names to accept (receive) in the current state
 (type: string or sequence of string
) | 
|  | defer | message name or names to defer (queue) in the current state
 (type: string or sequence of string
) | 
|  | discard | message name or names to discard (drop) in the current state
 (type: string or sequence of string
) | 
| Note | unlike other wait conditions, when a message is received, a Messageinstance is 
returned byget_event(), not theWaitForMessagesinstance. |