title: Understanding a regular expression \?[A-Z]{2}[a-z]{2}[0-9]{2}!
body: <p>I am little confused with following regular expression in python.I understand [A-Z]{2}[a-z]{2}[0-9]{2} part of it,but could not understand what /? and trailing ! mean.</p>
  
  <pre><code>\?[A-Z]{2}[a-z]{2}[0-9]{2}!
  </code></pre>
  
  <p>Can someone give me valid examples.Also ,does the regular expression interpretation vary according to language?(java,python etc)</p>