What do parent_parallel_id and parent_parallel_start_node_id mean in the class named after GraphParallel?

[hunter2009pf]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

I want to understand the running mechanism of dify workflow.
I know GraphParallel class is used for parallel running workflow.
My question: what do parent_parallel_id and parent_parallel_start_node_id mean in the class named after GraphParallel?

2. Additional context or comments

No response