Message
xref
has @ref-type="en" but does not point to a fn element with attribute fn-type="endnote".
Rule XPath:
This rule REPORTS an alert when the following is TRUE:
@ref-type = 'en' and not(every $rid in tokenize(@rid, '\s+') satisfies key('element-by-id',
$rid)[self::fn/@fn-type='endnote'])