regular expression help

[angrytuna]

Hello,
I'm semi-decent with regular expressions, but this one's got me stumped. I need a regular expression that takes a string $s, and breaks it up so that the substrings are no longer than 255 characters, but also end on word boundaries; i.e. if $s ended with "...not realistic", and the c in realistic was the 256th character, then the substring would end in "not".

What I'm looking at is:

preg_split([some regular expression],$s);

Can anyone help with [some regular expression]?

AT

[dalecosp]

Why use a regexp? Does anyone think that's faster? (Hey, not criticism, I'd really like to know, myself...)

OTOH, is this anything like what you want? from user-contrib notes at manual on 'substr'...

function substr_index($text, $maxChars = 255, $splitter = ' ') {
    $theReturn = $text;
     $lastSpace = false;

// only do the rest if we're over the character limit
    if (strlen($text) > $maxChars)    {
         $theReturn = substr($text, 0, $maxChars - 1);

// add closing punctuation back in if found
        if (in_array(substr($text, $maxChars - 1, 1), array(' ', '.', '!', '?')))     {
           $theReturn .= substr($text, $maxChars, 1);
        } else {

// make room for splitter string and look for truncated words
           $theReturn = substr($theReturn, 0, $maxChars - strlen($splitter));
            $lastSpace = strrpos($theReturn, ' ');

// Remove truncated words and trailing spaces
            if ($lastSpace !== false)  {
                 $theReturn = substr($theReturn, 0, $lastSpace);
            }
// append the splitter string
            $theReturn .= $splitter;
        }
     }
    return $theReturn;
}?>

As far as a regular expression, I have to make a guess "[.]{1,255}[.|!|?|;|😐 ]$" ??