Solidity – Correct Way to Define Custom Errors in Smart Contracts

I am someone new to Solidity and going through the custom errors part with REVERT I have found examples where the word "ERROR" is thrown inside CONTRACT

pragma solidity 0.8.18;

contract EjercicioSemana4 {
    // definir address 'admin' con valor de 0x08Fb288FcC281969A0BBE6773857F99360f2Ca06
    address public admin = 0x08Fb288FcC281969A0BBE6773857F99360f2Ca06;
    // definir boolean public 'pausado' con valor de false
    bool public pausado;

    error SaldoInsuficiente();
...
    function transferir(address _destinatario, uint256 _cantidad) public {
        if (_cantidad >= balances[msg.sender]) {
            revert SaldoInsuficiente();
        } else {
            balances[msg.sender] -= _cantidad;
            balances[_destinatario] += _cantidad;
            emit Transfer(msg.sender, _destinatario, _cantidad);
        }
    }

On the other hand, reviewing examples on the web as well as in the Solidity documentation I see that they declare the ERROR outside CONTRACT

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.4;

/// Insufficient balance for transfer. Needed `required` but only
/// `available` available.
/// @param available balance available.
/// @param required requested amount to transfer.
error InsufficientBalance(uint256 available, uint256 required);

contract TestToken {
    mapping(address => uint) balance;
    function transfer(address to, uint256 amount) public {
        if (amount > balance[msg.sender])
            revert InsufficientBalance({
                available: balance[msg.sender],
                required: amount
            });
        balance[msg.sender] -= amount;
        balance[to] += amount;
    }
    // ...
}

Are there any relevant differences in the definition of the ERROR statement outside or inside of CONTRACT?