title: Regular Expression - Validate Gmail addresses
body: <p>I am trying to create an expression to validate Gmail addresses.
  That's what I've done so far.</p>
  
  <pre><code>^([\w]*[\w\.]*(?!\.)@gmail.com)
  </code></pre>
  
  <p>I am trying to create an expression to validate Gmail addresses.
  That's what I've done so far.</p>
  
  <p>But it isn't working as I want.</p>
  
  <p>Gmail address:</p>
  
  <ol>
  <li>First and last character has to be [a-z0-9]</li>
  <li>The username contents only [a-z0-9.]</li>
  <li>There cannot be consecutive periods (i.e: <code>e..o@gmail.com</code> [This is wrong])</li>
  <li>There length of the username has to be between 6 and 30 letters.</li>
  </ol>
  
  <p>Being honest I don't have much experience with the Regular Expressions.</p>
  
  <p>By the way, is there a documentation for Regular Expression?</p>