title: xpath filtering items with a particular element
body: <p>I am not sure of the terminology so am having some trouble finding leads.<br>
  Basically suppose I have something like</p>
  
  <pre><code>&lt;book&gt;
     &lt;genre&gt;sci-fi&lt;/genre&gt;
     &lt;genre&gt;happy&lt;/genre&gt;
  &lt;/book&gt;
  &lt;book&gt;
     &lt;genre&gt;romance&lt;/genre&gt;
  &lt;/book&gt;
  </code></pre>
  
  <p>And I want to query for a list of books that don't have "sci-fi" as one of the genres.
  I tried something simple like</p>
  
  <pre><code>//book[//book/genre != "sci-fi"]
  </code></pre>
  
  <p>With the idea that it will return all of the books that do not have a genre element with "sci-fi" value, but it would still return the first one because one of its genre isn't "sci-fi"</p>
  
  <p>Also, how would I phrase this question in a way that people will have an idea what I am talking about?</p>