I couldn't find a graphical overlay demo on the net and I wanted to have a nice ornate way of displaying errors by simply calling a function. After a while of looking for one, I decided to create one myself. The outcome is that of a dimmed page with a table for the error message right in the center. You can customize it to suit your needs very easily. All you need to know is a little PHP and HTML. Nothing to it. I think the world needs a demo like this.
