sections:
This set of interfaces and contracts are all related to the ERC777 token standard.
For an overview of ERC777 tokens and a walkthrough on how to create a token contract read our ERC777 guide.
The token behavior itself is implemented in the core contracts: IERC777, ERC777.
Additionally there are interfaces used to develop contracts that react to token movements: IERC777Sender, IERC777Recipient.