title: Capture an optional group within another capture
body: <p>Given input like</p>
  
  <pre><code>${first_name}, ${last_name}, ${create_date:(Y-m-d)}, ${submit_date:(Y-m-d)}
  </code></pre>
  
  <p>I can use <code>\${(.*)}</code> to capture everything between the brackets.  When a suffix appears like on the dates in the example, I want to capture that as its own group.  How can I do that with one regular expression?</p>