"Whereas the first explanation implies a passive Web that accommodates all document formats equally, the second argues that the medium itself favors evolution from information capture towards knowledge representation. The key is that the Web can be leveraged reflexively to capture a document's structure and semantics -- that any community can define its own ontology, or adopt, extend, and combine others. In this context, we argue that the emergence of XML-based formats does not merely represent a slew of new competitors, but an ecosystem of interdependent document species."