een two rectangles.</p>
<p>If either rect is null, <a href="dart-ui/Rect/zero.html">Rect.zero</a> is used as a substitute.</p>
<p>The <code>t</code> argument represents position on the timeline, with 0.0 meaning
that the interpolation has not started, returning <code>a</code> (or something
equivalent to <code>a</code>), 1.0 meaning that the interpolation has finished,
returning <code>b</code> (or something equivalent to <code>b</code>), and values in between
meaning that the interpolation is at the relevant