title: Unable to read GET variable when used in $page_content
body: <p>I have a file called <code>productFocus.php</code> where I use the GET variable ID: <code>$id = $_GET["id"];</code>
  However this page is used in the <code>product.php</code> file in the following manner: </p>
  
  <p><strong>product.php</strong></p>
  
  <pre><code>&lt;?php
      $page_content = 'productFocus.php'; // $id = $_GET["id"];
      include('master.php');
  ?&gt;
  </code></pre>
  
  <p><strong>productFocus.php</strong></p>
  
  <pre><code>&lt;?php
      include "db/db.php";
      $id = $_GET["id"];
      $product = get_product_by_id($id);
  ?&gt;
  
  &lt;div class="product-focus"&gt;
      &lt;h3&gt;&lt;?php echo $product-&gt;name ?&gt;&lt;/h3&gt;
      &lt;img src="/images/products/&lt;?php echo $product-&gt;image ?&gt;"&gt;
      &lt;div id="description"&gt;
          &lt;h4&gt;Productinformatie&lt;/h4&gt;
          &lt;p&gt;&lt;?php echo $product-&gt;description ?&gt;&lt;/p&gt;
          &lt;h4&gt;Partners&lt;/h4&gt;
          &lt;table&gt;
              &lt;?php
                  foreach($product-&gt;partners_obj as $partner) {
              ?&gt;
              &lt;tr&gt;
                  &lt;td&gt;
                      &lt;a href=&lt;?php echo $partner-&gt;$product_url ?&gt; target="_blank"&gt;
                          &lt;img id="partner" src="/images/partners/&lt;?php echo $partner-&gt;image ?&gt;"&gt;
                      &lt;/a&gt;
                  &lt;/td&gt;
                  &lt;td&gt;
                      &lt;a href=&lt;?php echo $partner-&gt;$product_url ?&gt; target="_blank"&gt;&lt;?php $partner-&gt;$product_price ?&gt;&lt;/a&gt;
                  &lt;/td&gt;
              &lt;/tr&gt;
              &lt;?php
                  }
              ?&gt;
          &lt;/table&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><strong>master.php</strong></p>
  
  <pre><code>//HTML code
  ...
   &lt;?php include($page_content);?&gt;
  ...
  //HTML code
  </code></pre>
  
  <p>When I browse to <code>productFocus.php?id=324324</code> I can read the GET variable, but when I browse to <code>product.php?id=324324</code> I do not have access to the GET variable ID.</p>
  
  <p>Is there an elegant way to solve this issue?</p>