@StephenOTT I’m sorry I didn’t clear my question.
On the example parent-sub.bpmn model, a out mapping variable “MyResult” was setup for Multi-Instance task “Some Sub-Process” as follows.
But the user guide of Camunda said that " No output mapping for multi-instance constructs" and “The engine does not support output mappings for multi-instance constructs. Every instance of the output mapping would overwrite the variables set by the previous instances and the final variable state would become hard to predict.”.
See also link :https://docs.camunda.org/manual/7.11/user-guide/process-engine/variables/#multi-instance-io-mapping