Edit ACTION-1599: Write clarifying note in 6.1.3 to explain the non-impact of xsi:nil true on the definition of required MIP, rather than having the two rules for non-empty definition [recorded in http://www.w3.org/2009/05/13-forms-minutes.html#action01]: http://www.w3.org/2009/05/13-forms-minutes.html#action01