title: regex for integer or floating point number with two decimals
body: <p>I want to validate my currency field with regex. I want to allow the following pattern entries  </p>
  
  <pre><code>1.23
  1
  .45
  0.56
  56.00
  </code></pre>
  
  <p>No comma should be allowed. I've tried <code>\d+(\.\d\d)</code> but it allows only first, fourth and fifth entries. <code>\d+(?:\.\d\d+)?</code> allows all but third one.</p>