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 Property or Value after initializing the operation. Detailed return value information are available only, after the operation has been executed.