HTMLPurifier iFrame / regex issue

I am using the code provided on HTMLPurifier forums to allow support for iFrame tags, as Google, YouTube and others are now using iframe instead of embed for videos and maps.

Here is the code:

class HTMLPurifier_Filter_MyIframe extends HTMLPurifier_Filter
{
    public $name = 'MyIframe';

    public function preFilter($html, $config, $context) {
        return preg_replace("/iframe/", "img class=\"MyIframe\" ", $html);
    }

    public function postFilter($html, $config, $context) {
       $post_regex = '#<img class="MyIframe" ([^>]+)>#';
       return preg_replace_callback($post_regex, array($this, 'postFilterCallback'), $html);
    }

    protected function postFilterCallback($matches) {
        return '<iframe '.$matches[1].'></iframe>';
    }
}
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It almost works, except for one issue, this is the result:

<iframe height="275" src="omitted"></iframe> "class="MyIframe" >"

How can I get the class to be a part of the iframe tag?

UPDATE: Sorry, saw a matching question after posting.. initial search turned up nothing. Here is what had to change in the preFilter function:

return preg_replace("/iframe/", "img class=\"MyIframe\" ", preg_replace("/<\/iframe>/", "", $html));

Change the preFilter regex to:

return preg_replace("/iframe/", "img class=\"MyIframe\" ", preg_replace("/<\/iframe>/", "", $html));