Plug-In Detection
http://developer.apple.com/internet/webcontent/detectplugins.html

Apple Inc.
2006

Abstract:

Since there are clearly times when it makes sense to use a plug-in, the question arises of how to deal with those who don’t have the required plug-in installed. As Web developers, we have several choices. One option is to do nothing, simply serving the plug-in-dependent content. The trouble is that those that don’t have the required plug-in will get a rather disturbing page with a broken plug-in icon where your beautiful multimedia should be. Another option is to give visitors a choice between the plug-in version and the static HTML version of each page. Sometimes this may be the best choice, since it gives your visitors control over their experience. There are two problems, however. First of all, the choice itself interrupts a visitor’s experience of the site. Second, it requires them to know what plug-ins they have installed. But why should they need to know? Many users don’t know a plug-in from a spark plug? The final and often best option, the one this script is designed to help with, is to check to see if each visitor has a given plug-in. If they do, you can go ahead and serve them the page with the plug-in embedded.