s, in the
following format: <code>HH:MM:SS.mmmmmm</code>. For example,</p>
<pre class="language-dart"><code>var d = new Duration(days:1, hours:1, minutes:33, microseconds: 500);
d.toString();  // "25:33:00.000500"
</code></pre>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span></h2>
      <pre class="language-dart"><code class="language-dart">String toString() {
  String sixDigits(int n) {
    if (n &gt;= 100000) return &quot;$n&quot;;
    if (n &