title: XSLT select element with two different keys
body: <p>I'm trying to get an element with the following structure:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;pays&gt;
      &lt;pay id="23"&gt;
          &lt;accounts&gt;
              &lt;account id="2"&gt;
                  &lt;name&gt;Jonh&lt;/name&gt;
              &lt;/account&gt;
              &lt;account id="3"&gt;
                  &lt;name&gt;Mary&lt;/name&gt;
              &lt;/account&gt;
          &lt;/accounts&gt;
      &lt;/pay&gt;
  &lt;/pays&gt;
  </code></pre>
  
  <p>I want to get the account given key of the elements "pay" and "account".</p>
  
  <p>I tried to do:</p>
  
  <pre><code>&lt;xsl:key name="id_account" match="account" use="concat(@id,@id)"/&gt;
  </code></pre>
  
  <p>But this wrong and do not know to solve this situation.</p>