special values like <code>NaN</code> or <code>Infinity</code>, this method returns an
exponential representation (see <a href="dart-core/num/toStringAsExponential.html">toStringAsExponential</a>).</p>
<p>Returns <code>"NaN"</code> for <a href="dart-core/double/nan-constant.html">double.nan</a>, <code>"Infinity"</code> for <a href="dart-core/double/infinity-constant.html">double.infinity</a>, and
<code>"-Infinity"</code> for <a href="dart-core/double/negativeInfinity-constant.html">double.negativeInfinity</a