What does the "Send ..." setting of the delay node do?

The built-in delay node in rate-limiting mode has a setting with two options, "Send all topics" and "Send each topic in turn". What does it do?

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In the "for each msg.topic" mode - if say the node gets two messages - one with topic A and payload 1, and another with topic B and payload 2 - then in "send each topic in turn" mode at 1 second it will release the message with topic A and payload 1 - and then at the next second it will release the message with topic B and payload 2.... in "send all topics" mode it will release both messages at second 1.

So it essentially works as if I would multiply the time period by the number of unique topics I have?

I suppose that is one way to look at it...

It spaces each topic out by the time period, whereas send all sends whatever has accumulated at each time period.