Coordinating node - just enough information to perform aggregation

I am going through the documentation to better understand the role of coordinating node, the different phases of search request -

I come across a phase -

Each shard returns just enough information to the coordinating node

What sort of information this phrase refers - "just enough information" ?
If we had complex queries like bool queries, aggregation - I presume coordinating need to execute the same query again to aggregation the results globally, in that case, coordinate node will also have some come kind of lucene engine running to aggregate the results ?

No. the coordinating node only gets the result from each shard. It does not execute requests itself but merges the results coming from each shard.

For example, each shard returns 10 hits.
The coordinating node sorts them and returns to the user the best 10 hits.

ok, so in this case, "just enough information" refers to scoring values ?

It refers to: scores, 10 hits, computed aggs I believe.

Got it, is there any article about what parameters will be part of " Just Enough Information?

I can't remember if there's a blog post about it.

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