title: Check regex for letters numbers and underscore characters
body: <p>I tried to check if a string <em>Name</em> contains letters, numbers, and underscore character with
  the following code without success, any idea of what I miss here?</p>
  
  <p>var regex = new Regex(@"^[a-zA-Z0-9]+$^\w+$");</p>
  
  <pre><code>        if (regex.IsMatch(Name) )
  </code></pre>
  
  <p>....</p>
  
  <p>in addtion when I tried with the following code, I got a parsing error<br /><br /> <code>"^[a-zA-Z0-9\_]+$" - Unrecognized escape sequence \_.</code></p>
  
  <pre><code>Var regex = new Regex(@"^[a-zA-Z0-9\_]+$");
  </code></pre>