Hi,

highlight_* functions only highlight php code, because php code can be mixed with normal text or HTML.

That said, I like the feature request, like so:
highlight_string(string $source, bool $show_linenumbers)

FYI, it can be done like so:
<?php
ob_start();
highlight_string($source);
$out = ob_get_contents();
ob_end_clean();
$lines = explode("<br />", $out);
for($i=0; $i<count($lines);$i++)
{
    //needs tweaking of the font colors/tags
    printf("%03d: %s<br />", $i+1, $lines[$i]);
}
?>

you can also use the tokenizer extension - the code for doing highighlight_string type output can be derived from this.

http://docs.akbkhome.com/akpear/PHP_CodeDoc_Data.html#output_code

changing to wont fix - as the ability is already available using the tokenizer.