e same relative amount (see <a href="#TRICKY">&quot;TRICKY&quot;</a> section below).</p>

</dd>
<dt id="Return-value">Return value:</dt>
<dd>

<p>Error string, or undef on success and the input date/time string is shifted by the specified amount.</p>

</dd>
</dl>

<h1 id="SHIFT-STRING">SHIFT STRING</h1>

<p>Time shifts are applied to standard EXIF-formatted date/time values (eg. <code>2005:03:14 18:55:00</code>). Date-only and time-only values may also be shifted, and an optional timezone (eg. <code>-05:00<