title: xpath expression for when node doesn't exist?
body: <p>I am dealing with some irregularities in my documents, mainly, certain nodes are present and some other times, it's not there. I want an xpath which is able to take account both situations.</p>
  
  <p>For example across my documents, there are cases when span is present and when it's not there.</p>
  
  <pre><code>/html/body/span/div/table/tr/td/a
  /html/body/div/table/tr/td/a
  </code></pre>
  
  <p>How can I express an xpath which will match both cases above ?</p>