On 15 Apr 2014, at 00:32, Christian Roth <roth@visualclick.de> wrote:

Hi Florent,

  But this gives me the following error, even though QName are
comparable (unless I am mistaken):

    XTDE1030: Non-comparable types found while sorting: Values
    are not comparable (xs:QName, xs:QName)


says that QName's 'ordered' fundamental facet is 'false'. Could this be it?

It's related, but not directly relevant. Strings, booleans, and URIs are unordered in XSD but ordered in XPath, while gYearMonth and friends are ordered in XSD but unordered in XPath.

Michael Kay