how do query engine determine which node

I read @anilmatcha 's course and it said this

"The Vector Index can be used when we wish to fetch top-K relevant documents passing a certain threshold of matching score."

But i'm not sure what it means. Can someone show an example?

Can i just make query engine fetch random node? I want to make a random article idea generator based on business's document and PDF. So i want them to get a random node, and GPT will generate topic based on that.

You can then use a list index maybe with a filter argument which can pick node according to a random algorithm

Yea, if you want a random node you could make a custom node postprocessor for a list index, that just randomly picks one node

Example of a custom node postprocessor in this thread from yesterday

https://discord.com/channels/1059199217496772688/1124363317645946951/1124372129438240879

Thank you all