What is the case where you need multiple contracts/results for a single transaction?

Question

I'm designing DB tables to save transactions of tron.
And I have a question about protobuf spec of tron api.

According to Tron.proto, a transaction has array of contracts/results. https://github.com/tronprotocol/protocol/blob/master/core/Tron.proto#L328 https://github.com/tronprotocol/protocol/blob/master/core/Tron.proto#L338

And there's a comment below.

only support size = 1, repeated list here for extension

I'd like to ask what this "extension" does mean.
And what is the case where you need multiple contracts/results for a single transaction?

Thank you.

Answer 1

Tron originally borrows(copies) many from EOS(which supports multiple actions in a single transaction).

Now, they are old unused codes. Never mind, the size always equals to 1. No extension at all. And there won't be any future extension.