Explain the concept of 'idempotence' in the context of RESTful API design, and provide a specific example of a request that should be idempotent.

In the context of RESTful API design, idempotence means that performing the same request multiple times has the same effect as performing it once. In other words, whether you call the API endpoint once or multiple times in a row, the end result on the server should be the same. This is important for reliability and fault tolerance, as it allows clients to safely retry requests without causing unintended side effects. Idempotent methods do not necessarily return the same response on subsequent requests (although they can), but they must ensure that the state of the server remains consistent regardless of how many times the request is made. HTTP methods that are commonly considered idempotent include: GET, HEAD, PUT, and DELETE. POST, on the other hand, is generally *notconsidered idempotent because it typically creates a new resource each time it's called. Example: A `PUT` request to update a user's email address should be idempotent. For instance, a `PUT` request to `/users/123` with the body `{'email': 'newemail@example.com'}` should set the user's email address to `newemail@example.com`, regardless of how many times the request is sent. If the request is sent multiple times, the user's email address will simply remain `newemail@example.com`. This contrasts with a non-idempotent request, such as a `POST` request to `/orders` to create a new order. Each time this request is sent, a new order will be created, even if the request body is the same. The key is that `PUT` replaces the resource at the specified URI, whereas `POST` creates a new resource. Another example is a `DELETE` request. Deleting a resource using `DELETE /posts/5` is idempotent because no matter how many times you send that request, after the first successful deletion, the resource is gone, and subsequent calls have no further effect (they might return a 404 Not Found error, but the state on the server doesn't change).