Retrieving some tags from a string parsed by htmlentities

I have a string already parsed by htmlentities function.

I need to be able to reverse the htmlentities function only for a certain tags.

Anyone knows how can i do it?

For example:

filtertag('<b>')

to

<a href="http://www.asdasd.com">Link</a>
<br><br><b>My bold text</b>

HTML:

Gives

<a href="http://www.asdasdasd.com">Link</a>
&lt;br&gt;&lt;br&gt;<b>My bold text</b>

HTML:

The function must be able to deal with any tag and reverse it.

 

Make an array of tags you want to reverse, such as:

function filtertag( $string ) {

$good_tags = array('&lt;b&gt;' => "<b>", '&lt;/b&gt;' => "</b>");

foreach($good_tags as $start => $end) {

 str_replace($start, $end, $string);

}

return $string;
}

PHP:

Hope that helps.

 

What if the tag works in a different way?
For example img may be <img src="" class="x" alt=""...>

The tag list is not fixed...its a variable that comes from admin settings.