openzeppelin-contracts/contracts/mocks/docs/utilities/Multicall.sol

// contracts/Box.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {Multicall} from "../../../utils/Multicall.sol";

contract Box is Multicall {
    function foo() public {
        // ...
    }

    function bar() public {
        // ...
    }
}