XSLT, 2nd Edition

[2.0] Set Operators—except, intersect, and union

One weakness of XPath 1.0 was the inability to compare sets of nodes. If we selected two node-sets with two XPath 1.0 expressions, it was difficult to tell which nodes were in both sets and which were in one set but not the other. XPath 2.0 has two new set operators, except and intersect. If you enjoy extra typing, XPath 2.0 also adds the union operator, a synonym for the vertical bar operator (|) in XPath 1.0. (The vertical bar is still supported in XPath 2.0.)

Be aware that these operators work only on sequences of nodes. If you try to use them with sequences that contain atomic values, you’ll get an error.

As we discuss these operators, we’ll use this XML document:

<?xml version="1.0" encoding="utf-8"?>
<!-- books.xml -->
<favorite-books>
  <booklist>
    <book isbn="0596000537" 
      favorite="Doug Sheri">XSLT</book>
    <book isbn="0141439777" 
      favorite="Doug">Tristram Shandy</book>
    <book isbn="0142437298" 
      favorite="Doug">Herzog</book>
    <book isbn="0679762108" 
      favorite="Doug Sheri">The Sportswriter</book>
    <book isbn="0143035479" 
      favorite="Sheri">The Girls' Guide to Hunting and Fishing</book>
    <book isbn="0375724443" 
      favorite="Sheri">Ava's Man</book>
  </booklist>
</favorite-books>

We’ll select two sequences in our sample stylesheets: the books I like (the favorite attribute contains the string Doug) and the books my wife likes (the favorite attribute contains the string Sheri). We’ll use those two sequences to illustrate the set operators.

Note

The except ...