let $reults :=
(
  let $pKeywords := ('best clients', 'Very', '20')
  return
    for $kw in $pKeywords
    return
    (
      /*/entry[contains(comment, concat('!', $kw))],
      /*/entry[contains(comment, $kw)]
    )
  [not(position() gt 2)]
)
for $i in (1 to count($results))
return
(
  subsequence($results/comment, $i, 1),
  subsequence($results/buyer, $i, 1)
)

返回正确的解决方案:

<comment>The client is only 20 years old.  Do not be surprised by his youth.</comment>
<buyer/>
<comment>Very personable.  One of our best clients.</comment>
<buyer/>
<comment>!Very difficult to reach, but one of our top buyers.</comment>
<buyer/>
<comment>A bit of an eccentric.  One of our best clients.</comment>
<buyer/>