title: Pretty printing JSON isn't working
body: <p>I am trying to pretty print JSON currently in PHP, I have looked at the threads like <a href="https://stackoverflow.com/questions/6054033/pretty-printing-json-with-php">Pretty-Printing JSON with PHP</a> this but it does not work. I am on PHP 7.0.8-0ubuntu0.16.04.3 </p>
  
  <p>Code:</p>
  
  <pre><code>&lt;form method="POST"&gt;
      &lt;textarea name="json_data" id="json_data"&gt;
          &lt;?php
              if(isset($_POST['json_data'])){
                  echo json_encode($_POST['json_data'], JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
              }
          ?&gt;
      &lt;/textarea&gt;
  
      &lt;input type="submit" value="Pretty Print JSON"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>"[{\"title\":\"The Chainsmokers - Closer (Lyric) ft. Halsey\",\"length\":262000,\"id\":\"PT2_F-1esPk\",\"requester\":\"158310004187725824\",\"guildId\":\"226785954537406464\"}]"
  </code></pre>
  
  <p>Input JSON</p>
  
  <pre><code>[{"title":"The Chainsmokers - Closer (Lyric) ft. Halsey","length":262000,"id":"PT2_F-1esPk","requester":"158310004187725824","guildId":"226785954537406464"}]
  </code></pre>
  
  <p>For some reason the options <code>JSON_PRETTY_PRINT</code> and <code>JSON_UNESCAPED_SLASHES</code> do not actually work. Why is that? These are from PHP 5.4 and I am on PHP 7.</p>