title: Xpath condition get parent
body: <p>Here's my xml:</p>
  
  <pre><code>&lt;people&gt;
  &lt;person id="0001"&gt;
      &lt;firstname&gt;Christopher&lt;/firstname&gt;
      &lt;lastname&gt;Shaw&lt;/lastname&gt;
      &lt;birthdate&gt;1975-02-23T21:24:46.000+02:00&lt;/birthdate&gt;
      &lt;healthprofile&gt;
          &lt;lastupdate&gt;2014-09-30T10:38:07.000+02:00&lt;/lastupdate&gt;
          &lt;weight&gt;84&lt;/weight&gt;
          &lt;height&gt;2.13&lt;/height&gt;
          &lt;bmi&gt;18.51&lt;/bmi&gt;
      &lt;/healthprofile&gt;
  &lt;/person&gt;
  &lt;person id="0002"&gt;
      &lt;firstname&gt;Brian&lt;/firstname&gt;
      &lt;lastname&gt;Tooley&lt;/lastname&gt;
      &lt;birthdate&gt;1987-10-19T08:18:59.000+02:00&lt;/birthdate&gt;
      &lt;healthprofile&gt;
          &lt;lastupdate&gt;2014-09-30T10:38:07.000+02:00&lt;/lastupdate&gt;
          &lt;weight&gt;98&lt;/weight&gt;
          &lt;height&gt;2.17&lt;/height&gt;
          &lt;bmi&gt;20.81&lt;/bmi&gt;
      &lt;/healthprofile&gt;
  &lt;/person&gt;
  &lt;/people&gt;
  </code></pre>
  
  <p>What I want to do using Xpath is to extract the firstname of those users which weight is equal to 80 for example. I can't get this to work.</p>