I often use XML::XSH2. Leaving perl aside, the XSH code would look like this:

open 823927.xml ;
register-namespace ani http://www.elsevier.com/xml/ani/ani ;
for &{ sort :n /ani:bibdataset/ani:item/ani:bibrecord/ani:item-info/an
+i:itemidlist/ani:itemid[@idtype="PUI"] }
  ls ancestor::ani:item
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