title: using regex with xml2?
body: <p>Consider this simple example</p>
  
  <pre><code>example_xml &lt;- '&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;file&gt;
  &lt;book&gt;
  &lt;text&gt;abracadabra&lt;/text&gt;
  &lt;node&gt;&lt;/node&gt;
  &lt;/book&gt;
  &lt;book&gt;
  &lt;text&gt;hello world&lt;/text&gt;
  &lt;node&gt;&lt;/node&gt;
  &lt;/book&gt;
  &lt;/file&gt;'
  
  myxml &lt;- xml2::read_xml(example_xml)
  </code></pre>
  
  <p>Now, running this works as expected</p>
  
  <pre><code>&gt; myxml %&gt;% xml_find_all('//book')
  {xml_nodeset (2)}
  [1] &lt;book&gt;\n  &lt;text&gt;abracadabra&lt;/text&gt;\n  &lt;node/&gt;\n&lt;/book&gt;
  [2] &lt;book&gt;\n  &lt;text&gt;hello world&lt;/text&gt;\n  &lt;node/&gt;\n&lt;/book&gt;
  </code></pre>
  
  <p>but looking for nodes whose <code>text</code> attribute contain <code>wor</code> does not.</p>
  
  <pre><code>&gt; myxml %&gt;% xml_find_all('//book[contains(@text, "wor")]')
  {xml_nodeset (0)}
  </code></pre>
  
  <p>What is the problem here? How can I use regex (or partial string matching) with <code>xml2</code> ?</p>
  
  <p>Thanks!</p>