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鉴于这种DTD XPATH最后一个元素:具有特定元素
<!ELEMENT root (t*)>
<!ELEMENT t (pay|gift)?>
<!ELEMENT pay EMPTY>
<!ATTLIST pay amount CDATA #IMPLIED >
<!ELEMENT gift (#PCDATA)>
<!ATTLIST gift amount CDATA #REQUIRED >
我怎么能由XPath查询到达最后礼物的金额?