XPath select based on child value(s)
<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>