title: Regular expression for allow only numbers
body: <p>I want to check the following with regular expression</p>
  
  <pre><code>{Today,Format}
  </code></pre>
  
  <p>Today - will be remains as it is.
  In the place of Format, we can allow the digits from 0 to 12.</p>
  
  <p>for example: we have to allow</p>
  
  <pre><code>{Today,0}
  {Today,1}
  {Today,2}
  ...
  {Today,12}
  </code></pre>
  
  <p>and also have to allow </p>
  
  <pre><code>{Today,}
  {Today,Format}
  </code></pre>
  
  <p>Please help me and also refer me to some site to develop my regular expression skills.</p>