[RegEx] Cut off function + close tag

[whisher06]

Hi.
I've got this function

function stringTransform($str,$len) { 
    if(strlen($str)>$len){ 
        preg_match("/^(?=(.{{$len},}?b))/s",$str,$chunked); 
        $str= $chunked[1].'...'; 
    } 
    return $str; 
} 
$testo = "<p>Opera powers the Web on any device.Surfe the full Web and create dynamic applications using Web technology with Opera 9 for Devices</p>"; 
echo stringTransform($testo,50);

I'd like to get somthing like this :o

<p>Opera powers the Web on any device.Surfe the full...</p>

Possible strings:

"<p>Opera powers the </p>"
"Opera powers the "
"<p>Opera <a href="url">here</a> powers the </p>"

Could you help me, please ?
I'm not know which way to turn 😃

Thanks in advance.

Bye.