Which address types are allowed for collateral inputs

Question

Collateral inputs are required to be added to a transaction when any Plutus script is executed within that tx (i.e. spending a Plutus address utxo or minting a Plutus policy asset).

Obvious that a collateral input cannot be from a Plutus script address, as spending them would require for the script to be executed, which then would require a different collateral to be used, in case the script fails.

But what address types are allowed for collateral inputs at all? Is it only general vkey addresses or Native script addresses are allowed as well (since they themselves don't require collateral to be spent)?

Answer 1

The payment credential for any address in a collateral input must be a vkey credential (so not even native script).

You can see this check in the feesOK function in Figure 2 of the Babbage spec. Or here in the implementation.