It seems, on the other hand, eXide of eXist-db in the online version
doesn't even grok some of the generate-id based attempts:

let $nodes := (1 to 10) ! parse-xml-fragment('<node>' || . ||
'</node>')/node(),
 B B B  $nodes := (1 to 5) ! $nodes,
 B B B  $ids := distinct-values($nodes ! generate-id(.))
returnB  $ids ! (function($id) {$nodes[generate-id(.) eq $id][1]})(.)

gives <node>1</node>

let $nodes := (1 to 10) ! parse-xml-fragment('<node>' || . ||
'</node>')/node(),
    $all-ids := $nodes ! generate-id(.)
return  $all-ids