> The "xs" namespace is a bit odd in that it's known to 
> processors, like the "xsl" namespace,  but unlike the xsl 
> namespace it makes it into the result tree and requires pruning.

The reason for this: if the "xs" namespace had been excluded by default, we
would have had do something special for users who want to generate something
like <d xsi:type="xs:date"/>.

Michael Kay
http://www.saxonica.com/