Plug-ins are dynamic code modules, native to a specific platform on which Netscape Navigator runs. The primary goal of the plug-in API is to allow existing platform dependent code to seamlessly integrate with and enhance Navigator's core functionality by providing support for new data types. The plug-in API is designed to provide the maximum degree of flexibility and be functionally equivalent across all platforms.
Plug-ins are intended to be complementary to platform-native inter-application architectures such as OLE and OpenDoc, and platform-independent programming languages such as Java. OLE and OpenDoc are powerful, general-purpose component software systems, and components developed for these systems are relatively complex and heavyweight; Netscape plug-ins are designed specifically to extend Netscape Navigator and are relatively simple and lightweight. Java applets are secure and inherently cross-platform, but developing applets requires coding in a new language with new development tools; Netscape plug-ins can be written in C or C++ using existing development tools, making it easier to leverage existing code and platform-specific OS capabilities.
With the current version of the Plug-in API, plug-ins are capable of:
Plug-ins can have one of two modes of operation: embedded or full-page. An embedded plug-in is a part of a larger HTML document, and is loaded by Navigator when the document is displayed. The plug-in is then visible as a rectangular subpart of the page. Embedded plug-ins are generally used for multimedia images relating to text in the page, such as Macromedia Shockwave.
A full-page plug-in is not part of an HTML page and is loaded by Navigator when the user opens a file of a MIME type registered by a plug-in, by clicking a URL to the file, dragging the file to the Navigator's icon, or opening the file from within Navigator. The loaded plug-in completely fills the Navigator page. Full-page plug-ins are commonly used for document viewers, such as Adobe Acrobat.
The Netscape user interface remains relatively constant regardless of which type of plug-in is used. The part of the application window that does not display plug-in data remains familiar to the Netscape user. In particular, the basic operations of Navigator, such as navigation, history, opening files and the like, apply to all pages, regardless of which plug-ins are required to view them. However, note that scroll bars are not displayed for a full-page plug-in; if scrollbars are necessary in full-page mode, they should be drawn by the plug-in.