The [marketing materials claim](https://erc721x.org) ERC721x is "Fully Backward Compatible" with ERC-721. If so then I would expect to see the code: contract ERC721X implements ERC721 at https://github.com/loomnetwork/erc721x/blob/master/contracts/Interfaces/ERC721X.sol.
The marketing materials claim ERC721x is "Fully Backward Compatible" with ERC-721.
If so then I would expect to see the code:
at https://github.com/loomnetwork/erc721x/blob/master/contracts/Interfaces/ERC721X.sol.