title: Regex, Number or Empty
body: <p>Can someone show me how to match 4 digits <strong>or</strong> nothing in Regex? I have been using RegexBuddy and so far i have come up with this but the help text is saying '<em>Or match regular expression number 2 below - the entire match attempt fails if this one fails to match</em>' in regards to the pattern after the pipe.</p>
  
  <p>I would like either of the two to provide a positive match.</p>
  
  <pre><code>^\d{4}|$
  </code></pre>