title: A regular expression that matches 25 chars and starts with digits
body: <p>I have a text field which I need to validate using a regex. My requirement is as follow:</p>
  <blockquote>
  <p><code>CCCCNNNNNN</code> or <code>CCCCNNNNNNN</code> (Template)</p>
  <p><code>1234ABCDEFG</code> or <code>123-ABCDEFG</code> (Example string)</p>
  </blockquote>
  <p>Rules:</p>
  <ul>
  <li>The whole string is maximum 25 characters</li>
  <li>The first four characters (CCCC) must be alphanumeric</li>
  <li>CCCC is 4 characters exactly and can be digits or number</li>
  <li>CCCC can have a dash sign as 4th character</li>
  <li>NNNNNNNNNNNN can be up to 21 characters and only numbers</li>
  </ul>
  <p>E.g. <code>AAAA</code> <code>1234</code> <code>A58-</code> is a valid string for CCCC.</p>
  <p>Here is my research notes:</p>
  <ul>
  <li>I will need to match numerics first</li>
  <li>I will need the <code>+</code> char to specify to match this pattern X times</li>
  <li>I will need to match letters after that for 8-9 spaces</li>
  </ul>
  <p>There is a wonderful post on RegEx patterns here:</p>
  <p><a href="https://stackoverflow.com/questions/4246077/simple-problem-with-regular-expression-only-digits-and-commas/4247184#4247184">Matching numbers with regular expressions — only digits and commas</a></p>
  <p>My goal is to apply this REGEX pattern to a text box Mask in a WinForms app.</p>