The Vision language is designed around the concept of communicating objects. A message is a request for an object to carry out one of its operations.
Some messages require parameters.
Message expressions always produce an object as a result. In the preceding example, the expression produces a new object which represents the list of companies that satisfied the criteria. A message expression includes a recipient object, a selector, and possibly some parameters. The Recipient is the object to which the message is sent. The Selector is the name of the message.