title: Output Buffering not Working using Meta Tags
body: <p>I've always used <code>php_flag output_buffering On</code> so that I could <code>header("Location: ...")</code> after some html.</p>
  
  <p>Now that I've added <em>favicons</em>, <em>apple-touch-icons</em> and <em>og/twitter</em> I get this error:</p>
  
  <pre><code>Uncaught ErrorException: Cannot modify header information - headers already sent by (output started at *file name 1*_*row* in *file name 2*:*row*
  Stack trace:
  #0 [internal function]: {closure}(2, 'Cannot modify h...', '*file name 1*', *row*, Array)
  #1 *file name 2*(*row*): header('Location: ./log...')
  #2 {main}
  thrown in &lt;b&gt;*file name 2*&lt;/b&gt; on line &lt;b&gt;*row*&lt;/b&gt;&lt;br /&gt;
  </code></pre>
  
  <p>Which is the error I get when you try to send an header like a cookie (in this case <code>header("Location: ...")</code>) after something has already been sent.</p>
  
  <p>This seemed strange, so I did some tests. I found out that some <em>meta tags</em> cause this error even if <code>php_flag output_buffering</code> is set to `On</p>
  
  <pre><code>&lt;link rel="manifest"&gt;
  &lt;link rel="apple-touch-icon"&gt;
  &lt;link rel="icon"&gt;
  &lt;link rel="shortcut icon"&gt;
  &lt;link rel="mask-icon"&gt;
  
  &lt;meta itemprop="name" property="og:title" name="twitter:title"&gt;
  &lt;meta itemprop="description" property="og:description" name="twitter:description"&gt;
  &lt;meta itemprop="image" property="og:image" name="twitter:image"&gt;
  &lt;meta property="og:url" name="twitter:url"&gt;
  
  &lt;meta property="og:site_name"&gt;
  &lt;meta property="og:type"&gt;
  &lt;meta property="og:image:width"&gt;
  &lt;meta property="og:image:height"&gt;
  &lt;meta property="og:image:type"&gt;
  &lt;meta property="og:locale"&gt;
  </code></pre>
  
  <p>If one of these tags (one is enough) is present inside the <em></em>, <code>php_flag output_buffering</code> stops working.</p>
  
  <p>But it's not the same with any other tags, such as <code>&lt;meta property="og:see_also"&gt;</code> or <code>&lt;meta name="thumbnail"&gt;</code>. I can leave them and everything works properly.</p>
  
  <p>What's wrong with these tags? I obviously can't remove all them.</p>
  
  <p>My server is running on a Linux Server, with PHP 7.3 and Apache Module. Ask me for additional informations</p>