Re 2: HG doesn't have a published data model. I believe they have created 2 or 3 models at this point so far, but I happens under the hood. They can do this as

Re 2: HG doesn't have a published data model. I believe they have created 2 or 3 models at this point so far, but I happens under the hood. They can do this as there is only 1 implementation of HG, so no need to worry about compatible as much.