Core_Email::word_wrap

public function word_wrap($str, $charlim = '')
{
    // Se the character limit
    if ($charlim === '')
    {
        $charlim = ($this->wrapchars === '') ? 76 : $this->wrapchars;
    }

    // Reduce multiple spaces
    $str = preg_replace('| +|', ' ', $str);

    // Standardize newlines
    if (strpos($str, "\r") !== false)
    {
        $str = str_replace(array("\r\n", "\r"), "\n", $str);
    }

    // If the current word is surrounded by {unwrap} tags we'll
    // strip the entire chunk and replace it with a marker.
    $unwrap = array();
    if (preg_match_all('|(\{unwrap\}.+?\{/unwrap\})|s', $str, $matches))
    {
        for ($i = 0, $c = count($matches[0]); $i < $c; $i++)
        {
            $unwrap[] = $matches[1][$i];
            $str = str_replace($matches[1][$i], '{{unwrapped'.$i.'}}', $str);
        }
    }

    // Use PHP's native public function to do the initial wordwrap.
    // We set the cut flag to false so that any individual words that are
    // too long get left alone. In the next step we'll deal with them.
    $str = wordwrap($str, $charlim, "\n", false);

    // Split the string into individual lines of text and cycle through them
    $output = '';
    foreach (explode("\n", $str) as $line)
    {
        // Is the line within the allowed character count?
        // If so we'll join it to the output and continue
        if (strlen($line) <= $charlim)
        {
            $output .= $line.$this->newline;
            continue;
        }

        $temp = '';
        do
        {
            // If the over-length word is a URL we won't wrap it
            if (preg_match('!\[url.+\]|://|wwww.!', $line))
            {
                break;
            }

            // Trim the word down
            $temp .= substr($line, 0, $charlim-1);
            $line = substr($line, $charlim-1);
        }
        while (strlen($line) > $charlim);

        // If $temp contains data it means we had to split up an over-length
        // word into smaller chunks so we'll add it back to our current line
        if ($temp !== '')
        {
            $output .= $temp.$this->newline;
        }

        $output .= $line.$this->newline;
    }

    // Put our markers back
    if (count($unwrap) > 0)
    {
        foreach ($unwrap as $key => $val)
        {
            $output = str_replace('{{unwrapped'.$key.'}}', $val, $output);
        }
    }

    return $output;
}