title: Need to limit the number of character in a regular expression
body: <p>I'm writing a <a href="http://en.wikipedia.org/wiki/Regular_expression" rel="nofollow">regex</a>. At this point it allows any number of digits:</p>
  
  <pre><code>^(([1-9]*)|(([1-9]*).([0-9]*)))$
  </code></pre>
  
  <p>How do I allow exactly 64 digits at total?</p>