Today's browsers provide a lot of built-in functionality; however, there are many things they cannot do unaided, such as playing video or sound. Functionality of this sort is quite common on the Internet, and plug-ins and their ability to extend browser functionality make it possible to enjoy a richer web experience.
Plug-ins are downloaded applications and, as their name suggests, "plugged into" the browser. Many different plug-ins exist today; the more common ones include Adobe Flash Player, Microsoft's Silverlight, and Apple's QuickTime player.
Essentially, plug-ins are objects that encapsulate all the functionality they need to perform their tasks, such as playing audio files, in a way that hides the complexity from the website author. They are usually written in languages such as C++ and Java.
Plug-ins usually, but not always, have some sort of user interface. For example, the QuickTime plug-in has a user interface that displays buttons to play/pause the audio or video file, a seek bar to go to a precise point in the playback, and a volume control (see Figure 13-1.
Figure 13.1. Figure 13-1
window object or the Document Object Model. For example, the QuickTime player plug-in ...