The ERC721 NFT standard API interface

The specification of the ERC721 standard interface that we are discussing in this section is taken from the EIP standard document at https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md.

The ERC721 NFT standard interface is defined as follows:

interface ERC721 is ERC165 {
    event Transfer(address indexed _from, address indexed _to, 
                   uint256 indexed _tokenId);

    event Approval(address indexed _owner, address indexed _approved, 
                   uint256 indexed _tokenId);


    event ApprovalForAll(address indexed _owner, address indexed _operator, 
                         bool _approved);

    function balanceOf(address _owner) external view returns (uint256);

    function ownerOf(uint256 _tokenId) external view returns (address);

    function safeTransferFrom(address _from, address _to, 
                         ...