DN404 identification about dn404 HOT 3 OPEN

function _getMirrorERC721(address possibleDN404) internal view returns (address result) {
    assembly {
        mstore(0x00, 0x4ef41efc) // `mirrorERC721()`.
        if and(
            gt(returndatasize(), 0x1f),
            staticcall(gas(), possibleDN404, 0x1c, 0x04, 0x00, 0x20)
        ) {
            // If result is a non-zero address, contract is very likely DN404.
            result := shr(96, mload(0x0c)) 
        }
    }   
}