Complete, general form validation

This script is a combination of a lot of common form validation elements - checking for non-entries, image swaping to indicate invalid entries, focusing on invalid fields, and feedback to the user through an alert box. I got tired of writing new code for every form (or even cutting and pasting a lot) so this is intended as a .js include file, and all the information necessary to validate the form is contained in the form itself. Most validation is of the did-they-fill-it-in variety. See the comments in the script for more details. Additional validation can be performed with a customized object-oriented JavaScript function. Explanations and an example are provided in the comments.