title: The generation from html to xls. Warning "The file format differs from the format that the file name extension specifies"
body: <p>Generated xls file opens(in MS Excel 2013) with warning </p>
  
  <blockquote>
    <p>The file format differs from the format that the file name extension
    specifies</p>
  </blockquote>
  
  <p>, if press "Yes" - file perfectly opens, but I would like without this warning.
  The code fragment:</p>
  
  <pre><code>header("Content-Type: application/vnd.ms-excel; charset=windows-1251");
  header("Expires: 0");
  header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
  header('Content-Disposition: attachment; filename=filename.xls);
  
  echo&lt;&lt;&lt;HTML
  &lt;html&gt;
  &lt;head&gt;
  &lt;meta http-equiv="content-type" content="text/html; charset=windows-1251" /&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;table border="1" cellspacing="0" cellpadding="0"&gt;
  /* many lines */
  &lt;/table&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  HTML
  die();
  </code></pre>