In developing these slide shows, we learned quite a bit about the differences between Web browsers. For example, we make use of layers , which allow different images to be placed on top of one another, with transparent areas that allow the lower layers to be seen. Layers can also be moved around on the screen. To show a cursor, we create a rectangular layer with the image of a cursor. The parts of the rectangle that are not part of the cursor are transparent, so the image underneath shows through.
Layers are a very powerful way to show graphic images on a Web page.
Unfortunately, different browsers require different programming to create and move the layers. Netscape created one way of doing it and Microsoft created another, so a Web page will only work on both Netscape Navigator and Internet Explorer if it detects the type of browser and uses different programming for each one. We also found that any programming error, such as sending an Internet Explorer-style command to Netscape Navigator, can cause the entire page to stop working. We tested our slide shows with Netscape Navigator 4.77, Internet Explorer 5.50, and Netscape Navigator 6.01. These are the latest browser versions from Netscape and Microsoft.