使用HTML.Allowed时，HTMLPurifier会消耗大量内存吗？

I have the following string:

<p>
    This is a test
</p>
<p>
    More test text.
</p>
<p>
    <a href="http://www.google.com/">google</a>
</p>

When I run that through HTMLPurifier using this code:

require_once(__DIR__ . '/../libraries/htmlpurifier-4.6.0-lite/library/HTMLPurifier.auto.php');
$config   = \HTMLPurifier_Config::createDefault();
$config->set('HTML.Allowed', 'code,span,div,label,a,br,p,b,i,del,strike,u,img,video,audio,blockquote,mark,cite,small,ul,ol,li,hr,dl,dt,dd,sup,sub,big,pre,code,figure,figcaption,strong,em,table,tr,td,th,tbody,thead,tfoot,h1,h2,h3,h4,h5,h6');
$purifier = new \HTMLPurifier($config);
$sanitized = !empty($_POST['text'])?$purifier->purify($_POST['text']):null;

I get the error:

Allowed memory size of 134217728 bytes exhausted (tried to allocate 51746711 bytes)

Why is this happening?

EDIT:

Changing the config line to this:

$config->set('HTML.Allowed', 'code,span,div,label');

Results in this error:

Allowed memory size of 134217728 bytes exhausted (tried to allocate 37415543 bytes)