http://www.w3.org/TR/xpath-full-text-10/#sec-ftnot:

The following expression returns book elements containing "web site usability" but not "usability testing":

//book[. ftcontains "web site usability" ftand 
ftnot "usability testing"]


This is NOT correct because the example document does NOT have "web site usability". Although this text appears in the value of attribute shortTitle,
however, attribute value contents is NOT part of the //book atomization.
Also, the document contains "usability testing" text, so ftnot is false.

The example document is at
http://www.w3.org/TR/xpath-full-text-10/#ftselections
with following contents:
<books>
  <book number="1">
    <title shortTitle="Improving Web Site Usability">Improving  
        the Usability of a Web Site Through Expert Reviews and
        Usability Testing</title>
    <author>Millicent Marigold</author>
    <author>Montana Marigold</author>
    <editor>Véra Tudor-Medina</editor>
    <content>
      <p>The usability of a Web site is how well the  
          site supports the users in achieving specified  
          goals. A Web site should facilitate learning,  
          and enable efficient and effective task  
          completion, while propagating few errors.
      </p>
      <note>This book has been approved by the Web Site  
          Users Association.
      </note>
    </content>
  </book>
</books>