$this</span><span class="o">-&gt;</span><span class="na">output</span><span class="o">-&gt;</span><span class="na">set_header</span><span class="p">(</span><span class="s1">&#39;Last-Modified: &#39;</span><span class="o">.</span><span class="nb">gmdate</span><span class="p">(</span><span class="s1">&#39;D, d M Y H:i:s&#39;</span><span class="p">,</span> <span class="nv">$last_update</span><span class="p">)</span><span class="o">.</span><span class="s1">&#39; GMT&#39;</span><span class="p">);</span>
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