Detect last post-grouping tuple - xquery

Question

In XQuery 3.0, how is it possible to detect the last post-grouping tuple (defined by XQuery 3.0 spec) produced by the return clause? Is it possible to use something like position() = last()? What would be the context for the position function?
For example, say I want to generate CSV output via XQuery. In order to separate lines in the CSV output, I append a new-line after each tuple produced by the return clause:
xquery version "3.0";
declare option saxon:output "omit-xml-declaration=yes";
declare option saxon:output "method=text";
declare variable $data := (
<items>
<item>
<property name="a"/>
<property name="a"/>
<property name="b"/>
</item>
<item>
<property name="a"/>
</item>
<item>
<property name="b"/>
<property name="c"/>
<property name="d"/>
</item>
<item>
<property name="b"/>
<property name="c"/>
</item>
</items>
);
for $item in $data/item,
$name in $item/property/#name
group by $name
return (
text{string-join(($name, string(count($item))), ",")},
text{"
"}
)
However, this leaves an empty line after the last tuple. If I could test for the tuple position, I could avoid appending new-line after the last tuple.

Answer 1

The XQuery specs indeed seem to be missing something like group by $variable at $position here, similar what would be allowed in the for clause. Reading up the XQuery 3.0 specs again, I couldn't find anything that would help, either. position() and last() require a node context, which is not available within loops.
But regarding your underlying problem: why not use another string-join(...) to concatenate the items with newlines in-between, similar to like you did for the counts?
string-join(
for $item in $data/item,
$name in $item/property/#name
group by $name
return (
text{string-join(($name, string(count($item))), ",")}
),
text{"
"}
)