title: Regular expression for twitter username
body: <p>I need a javascript regular expression to match twitter usernames.</p>
  
  <p>The username is entered by the user while signing up, so I don't want to distract them with too many error notifications. Because of that, I need the expression to match valid usernames regardles if they have the @ before the username or not.</p>
  
  <p>Twitter usernames can contain latin characters, underscores and numbers, and the only limitation is the can be up to 15 characters long. ( but I need the regex to match 16 characters as well, in case someone enters the @ before the username ).</p>