xml - How can I select an element with multiple classes with Xpath?

Question

In the above xml sample I would like to select all the books that belong to class foo and not in class bar by using xpath.

<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>
  <book class="foo">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book class="foo bar">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book class="foo bar">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
</bookstore>

Answer 1

By padding the @class value with leading and trailing spaces, you can test for the presence of " foo " and " bar " and not worry about whether it was first, middle, or last, and any false positive hits on "food" or "barren" @class values:

/bookstore/book[contains(concat(' ',@class,' '),' foo ')
        and not(contains(concat(' ',@class,' '),' bar '))]