title: How to detect exact length in regex
body: <p>I have two regular expressions that validate the values entered.</p>
  
  <p>One that allows any length of Alpha-Numeric value:</p>
  
  <pre><code>@"^\s*(?&lt;ALPHA&gt;[A-Z0-9]+)\s*"
  </code></pre>
  
  <p>And the other only allows numerical values:</p>
  
  <pre><code>@"^\s*(?&lt;NUM&gt;[0-9]{10})"
  </code></pre>
  
  <p>How can I get a numerical string of the length of 11 not to be catched by the <code>NUM</code> regex.</p>