VBScript is a natural choice for application developers currently using Visual Basic or Visual Basic for Applications (VBA). The downside is that only Internet Explorer natively supports VBScript, although there is a plug-in (see the sidebar entitled "Plug-in Technology") for VBScript in Netscape Navigator.
Plug-ins are software components that are used to dynamically extend the document content types that a Web browser understands. For example, there are plug-ins that allow the user to load audio, video, word processor and spreadsheet documents, and even new scripting engines into the browser.
A plug-in is associated with one or more MIME types. When the browser encounters an embedded type in a Web page that requires a plug-in, it checks for a matching plug-in, instantiates it, and passes the media reference to the plug-in. The plug-in is then responsible for the appropriate processing of the media.