Issue - 63 - For Each?

The following are thoughts I've had on how we could address issue 63. 
Although these thoughts are still fairly rough I wanted to release them 
now because 63 is on the agenda for the F2F. Since these are early 
thoughts I reserve the right to disavow them at any time.

I thought an easy way to provide the feature asked for in 63 is to 
provide a macro that has proven its utility in numerous structured 
languages - For Each.

I was thinking of a syntax like:
<foreach sourceVariable="ncname" part="ncname"? \
          iteratorVariableName="ncname" iteratorVariableType="qname"
          standard-attributes>
    standard-elements
    <query language="anyURI">...</query>
    activity
</foreach>

The idea is that the query element would be an expression that generates 
zero or more nodes. Each generated node would be assigned to a local 
variable whose name is given in iteratorVariableName and whose type is 
iteratorVariableType. The foreach would then walk through each node one 
by one in document order. If no nodes are returned then the activity 
would do nothing.

For example:
foreach sourceVariable="orderManifest" part="somePart"\
         iteratorVariableName="anOrder" iteratorVariableType="b:ar"
    query language="http://www.w3.org/TR/1999/REC-xpath-19991116"
       ordermanifest/orders
    ...

Would be a Macro for:
scope
    variables
       variable name="anOrder" type="b:ar"
       variable name="currentInstanceNum" type="xs:int"
    sequence
       assign
          copy
             from
                "1"
             to variable="currentInstanceNum"
       while condition="$currentInstanceNum <=\
                        count($orderList/somePart/ordermanifest/orders)"
          assign
             copy
                from variable="orderList" part="somePart"
                   query
                      "(/ordermanifest/orders)[$currentInstanceNum]"
                to variable="anOrder"
          assign
             copy
               from
                  expression
                     "$currentInstanceNum+1"
               to variable="currentInstanceNum"
          ...