We need an extension to DFDL to allow schema authors to declare they would like a element child to instead appear in an XML-conversion of the DFDL infoset as an XML attribute.

So instead of <foo><bar>1</bar><baz>2</baz></foo>, you can get the more human friendly <foo bar="1" baz="2"/> as the XML-conversion.

The property cannot be in the DFDL property namespace; hence daffodil: prefix, not dfdl: prefix:

Possible names: daffodil:asXMLAttribute="true" or daffodil:XMLConversion="asAttribute"