The display of .gif and jpg image files are examples. External are displayed in a separate window by a helper app. An example would be an Adobe Acrobat document. The browser has a table of file extensions that are mapped to a type of application. Browsers can be set up to use a specific helper app for each type of application.
Most browsers come with a default list of helper apps, and users can add to the list.
The applications themselves must be installed in order to work. If you have a captive audience and you want to use a particular type of media, you can provide them with information on obtaining and configuring necessary helper apps. They would download the software then add a 'New Type' to the Applications helper list. For more information see HTML for the World Wide Web , page 206. All rights reserved.