The W3C HyperText Coordination Group has published an initial Component Extension (CX) API Requirements specification to address the processing of compound documents. This W3C Note "describes requirements for browser plug-ins and an active component architecture for the Web for server and client software. The term 'Component Extension' in this context (also well-known as plug-ins in Web browsers) refers to any software in charge of providing the client-side part of the Component Extension API; it is a program that runs as part of the Host implementation and that is not part of content." The API requirements specification is motivated by the need to support additional content types in compound documents: now that "we have several XML languages used to represent different parts of Web pages (e.g., XHTML, SVG, MathML, XForms, etc.), we need a well defined mechanism that allow different specialized tools to work together and handled these compound documents." Server-client coordination must address the mixing of multiple XML Namespaces and default/fallback client behaviors in cases where component extensions are unavailable.

Bibliographic information: Component Extension (CX) API requirements Version 1.0. W3C Note 11-December-2001. Edited by Angel Diaz (IBM), Jon Ferraiolo (Adobe), Stein Kulseth (Opera), Philippe Le Hégaret (W3C), Chris Lilley (W3C), Charles McCathieNevile (W3C), Tapas Roy (Openwave), and Ray Whitmer (Netscape/AOL). Version URL: http://www.w3.org/TR/2001/NOTE-CX-20011211. Latest version URL: http://www.w3.org/TR/CX.

Examples of API requirements topics: formatting, rendering, style, error handling, events, DOM core tree, starting point, connecting with outside/scripting, nesting/reetrance, abstraction level, editing, associations/registrations/negotiations, accessibility, versioning, storage/persistence, memory management, security.