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XML Query Use Cases: http://www.w3.org/TR/xquery-use-cases/
Copyright ©2003 World Wide Web Consortium, (Massachusetts Institute of Technology, European Research Consortium for Informatics and Mathematics, Keio University). All Rights Reserved. This work is distributed under the W3C® Software License [1] in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
[1] http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231
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 Filename: treeQ1.xq 
 Section:   1.2.4.1 Q1  
 Purpose:   Prepare a (nested) table of contents for Book1, listing all the sections  and their titles. Preserve the original attributes of each <section> element, if any. 
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declare function local:toc($book-or-section as element()) as element()*
{
    for $section in $book-or-section/section
    return
      <section>
         { $section/@* , $section/title , local:toc($section) }                 
      </section>
};

<toc>
   {
     for $s in doc("book.xml")/book return local:toc($s)
   }
</toc>