User spaces and receiver variables

APIs that return information to a caller generally return the information in a user space (used by list APIs) or a receiver variable (used by retrieve APIs).

• User spaces
  List APIs require a user space for returning information. A user space is an object consisting of a collection of bytes that can be used for storing any user-defined information.
• Receiver variables
  A receiver variable is a program variable that is used as an output field to contain information that is returned from an API.