A smart contract that describes visibility

visibility.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.17;

contract Visibility {
    uint256 private x = 0;
    uint256 internal y = 1;
    uint256 public z = 2;

    // Public 
    // Accesed from any smart contract, function inside 
    // its smart contract and web3 script
    function publicFunction() public pure returns (uint256) {

    }

    // Private
    // Accesed only from within the contract
    function privateFunction() private pure returns (uint256) {

    }

    // Internal
    // Accessed only from within the contract & child contracts
    function internalFunction() internal pure returns (uint256) {

    }

    // External 
    // Accessed only from any contract & web3 script 
    // but not from an internal function
    function externalFunction() external pure returns (uint256) {

    }

    function demo() external pure {
        privateFunction();
        internalFunction();
        publicFunction();
    }
}