例えば
<SCHOOL>
<STUDENT NAME="BOB">
<GRADE SCORE="50"/>
<GRADE SCORE="10"/>
<GRADE SCORE="20"/>
<GRADE SCORE="40"/>
<GRADE SCORE="90"/>
<GRADE SCORE="30"/>
</STUDENT>
</SCHOOL>
に変換
<SCHOOL>
<STUDENT NAME="BOB">
<GRADE SCORE="50"/>
<GRADE SCORE="10"/>
<GRADE SCORE="20"/>
</STUDENT>
<STUDENT NAME="BOB">
<GRADE SCORE="40"/>
<GRADE SCORE="90"/>
<GRADE SCORE="30"/>
</STUDENT>
</SCHOOL>
xslt を使い始めたばかりで、これを達成する方法がわかりません!