Dmitry Lenkov; Norman Walsh. <a href="http://www.w3.org/TR/2004/NOTE-proc-model-req-20040405"><cite>XML Processing Model Requirements.</cite></a> 5 April 2004. W3C Note. URL: <a href="http://www.w3.org/TR/2004/NOTE-proc-model-req-20040405">http://www.w3.org/TR/2004/NOTE-proc-model-req-20040405</a>