title: Regex - Match a string which has zero or one spaces
body: <p>I'm trying to match a string which starts with @, can contain any amount of letters or numbers but can only contain a maximum of one space (or zero spaces).  So far I have</p>
  
  <pre><code>@([A-Za-z0-9]+)
  </code></pre>
  
  <p>which matches the characters but without the space.  I think I need \s{0,1} but I'm not sure where to put it.. Can anyone help?</p>
  
  <p>Thanks.</p>