Oh, right, I forgot about the fact that it has to be able to go back and forth between bbcode and html. There's a file includes/class_wysiwygparser.php that goes from html to bbcode, and it uses the <font> tag instead of the font-size attribute. So you could either change your replacement to use the font tag (which I know isn't the way it's done these days), or else figure out how to change the code in class_wysiwygparser.php. I only glanced at it, but there's a function parse_style_attribute(), and it currently doesn't parse out the font size. You might be able to add a line to the $searchlist array to make it find the font size and insert a size tag for it. Probably something like: