What is ERC-998?
ERC-998 is an extension to the ERC-721 standard that adds the ability for non-fungible tokens to own other non-fungible tokens and ERC-20 tokens.
Non-fungible tokens that implement ERC998 also implement the ERC-721 standard.
The official ERC-998 standard is at this link: EIP-998
Articles About ERC-998
Introducing Crypto Composables
Crypto Composables — Building Blocks and Applications
ERC-998 and the Future of Blockchain Game Assets
ERC-998, The New Token On The Block
Top-Down and Bottom-Up Composables, What’s the Difference and Which One Should You Use?