Alex Milowski. <a href="http://www.w3.org/TR/2006/WD-xproc-requirements-20060411"><cite>XML Processing Model Requirements and Use Cases.</cite></a> 11 April 2006. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2006/WD-xproc-requirements-20060411">http://www.w3.org/TR/2006/WD-xproc-requirements-20060411</a>