title: XPath select based on child value(s)
body: <p>Here's some xml:</p>
  
  <pre><code>&lt;books&gt;
      &lt;book&gt;
          &lt;author&gt;Tom&lt;/author&gt;
          &lt;genres&gt;
              &lt;genre&gt;Science&lt;/genre&gt;
              &lt;genre&gt;Romance&lt;/genre&gt;
          &lt;/genres&gt;
      &lt;/book&gt;
      &lt;book&gt;
          &lt;author&gt;Mike&lt;/author&gt;
          &lt;genres&gt;
              &lt;genre&gt;Politics&lt;/genre&gt;
              &lt;genre&gt;Romance&lt;/genre&gt;
          &lt;/genres&gt;
      &lt;/book&gt;
  &lt;/books&gt;
  </code></pre>
  
  <p>How can I define an xpath such that it pulls all Romance books? Or maybe all Romance and Politics books?</p>