pre_replace() within HTML

[gerkintrigg]

I have the following code:

<?php
$html = '<b alt="bum">The word "bum" needs replacing with something less offensive.</b>';
$pattern = '@\>(.+?)\<@';

$replacement = '>'.str_replace('bum','bottom',$html).'<';

$page = preg_replace($pattern, $replacement, $html);

echo $page;
?>

 

If you run it, you'll find that the word "bum" is replaced with "bottom" which is what I want, but the original alt tag (and I know it's nonsense HTML) is also being duplicated, with the duplicate being replaced... though I don't know why it's showing twice...

 

I just want to keep the original HTML but replace its contents... any suggestions?