</code> with each element in <code>elements</code> in order.
If the call to <code>action</code> returns a <code>Future&lt;T&gt;</code>, the iteration waits
until the future is completed before continuing with the next element.</p>
<p>Returns a <a href="dart-async/Future-class.html">Future</a> that completes with <code>null</code> when all elements have been
processed.</p>
<p>Non-<a href="dart-async/Future-class.html">Future</a> return values, and completion-values of returned <a href="dart-async/Future-clas