How does signJSON work?

[July-Only]

// Signs a json transaction with private key.

I see that there is no use example and explanation of this method in your application document. I hope you can give some explanation and example of ETH. Thank you very much! The method is as follows:
public static func signJSON(_ json: String, key: Data, coin: CoinType) -> String

[optout21]

Maybe this helps?
https://github.com/trustwallet/wallet-core/blob/master/tests/Ethereum/TWAnySignerTests.cpp#L302