Web Standards Programmer's Reference: HTML, CSS, JavaScript®, Perl, Python®, and PHP

10.1. Understanding Plugins

Plugins are small applications that extend the capabilities of user agents by running on the client machine and handling data delivered via HTTP supplied by the user agent. A typical plugin works with a user agent as shown in the diagram in Figure 10-1.

Figure 10-1. Figure 10-1

The user agent requests the content as normal but receives a file it doesn't know how to deal with. However, it has a plugin registered for the file it receives. The browser launches the plugin and passes the file to the plugin for processing. The plugin presents the data to the user in an environment native to the data while remaining in the browser environment.

Note that plugins are specialized applications requiring the end user to install and maintain them on their system(s). Although plugins (especially Flash and the like) are common on the Web, you should use caution in deciding to use plugin-enabled content in your pages, as it does have an impact on the end user.

The first plugins enabled the Netscape browser to deliver content other than text and basic graphics. The earliest plugins included programs from Macromedia for its Shockwave product and from Adobe for its Acrobat (PDF) product. These programs enabled users to view Shockwave graphic presentations and Adobe PDF files.

Today plugins are available for almost all types of data. The old standbys are still available ...