If you visited the first form submission page you may recall that it was mainly concerned with the best method of handling submission as a result of pressing the [ENTER] key by mistake. That lesson briefly mentioned other methods of handing erroneous types of user input.
As you search the internet you can find various methods of FORM VALIDATION that can be used. MrKent.com has tried many of them over the years. What is presented here has been found to be the most reliable of all.
This page also provides the code and sample forms that illustrate the difference between good form design and poor form design. The code for the target PHP page has also been provided below.