Handling Form Submissions and Validating Data

Submit the comment form from the previous lesson, then press the browser's refresh button. The browser warns that it will send the form data again, and if the reader agrees, the same comment arrives a second time. The cause is that the thank-you page was the direct response to a POST request, and refreshing a page repeats the request that produced it.

This lesson fixes that problem first, and then turns to the other half of handling a submission: deciding which values to accept