ehind</code> window. Otherwise return <code>NULL</code>.</p><ul><li><p><strong>code</strong> a string of digits.</p></li>
<li><p><strong>t</strong> a POSIXct object or an integer that represents the number of seconds since UNIX epoch.</p></li>
<li><p><strong>behind</strong> a non-negative integer, the amount of time steps to look behind. A value of <code>1</code>
means to accept the code before <code>period</code> seconds ago.</p></li>
</ul><div class="sourceCode"><pre><code><span></span>
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