XQuery implementations

Hi,

Does anyone know of a open source XQuery implementation that can do the 
following statement:


for $quizes in document(/db/quiz/data)/quiz
    for $categories in $quizes/category
       for $questions in $categories/question
       where @id = 'a'
       return
       <quiz>
           {$quizes/@*}
            <category>
               {$categories/@*}
                     {$question}
            </category>
</quiz>


Thanks,

juha