From the early days of the World Wide Web, Web Agents had been extended to support more types of contents. The recent developments of XML and the possibility to mix mupltiple XML Namespaces in the document reiterated the need to extend implementations and relaying on add-on softwares to accomplish tasks not supported by default in the implementation. In other words, we have several XML languages to represent different parts of Web pages (XHTML, SVG, MathML, XForms, etc.), we now need a well defined mechanism that allow different specialized tools to work together and handled these compound documents.

This W3C Note contains a non-exhaustive list of requirements to work on a Component Extension API. The goal of this API is to extend the ability of a Web application. Note that the Web application can be either on the server side or on a client side, and does not automatically implies interaction with a user or having a Web browser.