When you see a skin, you are seeing only the surface. Behind the surface are several files that make up the complete skin. Technically speaking, a skin is a group of files, with each file containing a specific kind of information. Here are the types of files you can use to make up a complete skin.
If you want to create more complicated responses to events, you can create script files using Microsoft JScript. These are text files and have a .js file name extension.