At what level are Ricardian contracts implemented? Examples I see are in the constitution . Can these be applied at the application level? Eg. A derivation contract with the terms of contract richardian?
Yes, you can create a dapp with a Ricardian contract embedded in it. Specifically in the abi file which is a JSON file defining the interface of the smart contract or the dapp. This is the empty Ricardian structure:
A more elaborate example of a ricardian contract can be seen in the hello example contract.
A Ricardian contract states the intentions of the contract and can reference actual code from the dapp. More info can be found in: Ricardian contracts — legally binding agreements on the blockchain