set_operation - Field defines a set operation

The option is set for field definitions describing the return value of an operation (function or expression). When the operation is a set or collection operation operating on the complete set instead of a single selected instance, the option must be set to true . For instance operations operating on a single instance, the option is set to false . AUTO is set in order to indicate that the operation does not require a selected instance in the property handle.

The value is set to 2 in order to indicate a node changing action (Open, Close). In this case, the action changes the value of the calling property by creating a new node or removing the existing. The calling object need not to be valid, in this case.

3 indicates a handle operation, which returns a new property handle. Usually, the return value of handle operations is set to bool ( LOGICAL ) after initializing the operation. Detailed return value information are available only, after the operation has been executed.