Checking for valid entries
This script is somewhat special amongst scripts of its kind because this one allows names which have hyphens (a '-' is a hyphen) or apostrophes in them. Most people don't seem to allow that, even though there are many names that do have hyphens and apostrophes. However, it is still based on simple patterns and may not be able to cope some more complicated names or form configurations.
In browsers that cannot use JavaScript, the form will be submitted without performing any checks.
Be warned that you cannot rely on these checks to be fool-proof. If someone is determined to submit the form with invalid entries, they can easily disable JavaScript or, as I have done before, rewrite the page. You should back the checks up if possible with some checks performed on the server as well.
To download the script(s), see the script license, and check details like browser compatibility, use the links on the navigation panel at the top of this page.