title: Regex that does not match any html tag
body: <p>I am really bad with regexps, what I want is a regexp that does not match any html tags (for user input validation).</p>
  
  <p>What I want is negative of this:</p>
  
  <pre><code>&lt;[^&gt;]+&gt;
  </code></pre>
  
  <p>What I currently have is </p>
  
  <pre><code>public class MessageViewModel
  {
      [Required]
      [RegularExpression(@"&lt;[^&gt;]+&gt;", ErrorMessage = "No html tags allowed")]
      public string UserName { get; set; }
  }
  </code></pre>
  
  <p>but it does opposite of what I want - allows usernames only with html tags</p>