source: branches/rsr.v5.1.1/web/punbb/include/utf8/strspn.php

<?php

/**
* @version $Id: strspn.php,v 1.1 2006/02/25 13:50:17 harryf Exp $
* @package utf8
* @subpackage strings
*/

/**
* UTF-8 aware alternative to strspn
* Find length of initial segment matching mask
* Note: requires utf8_strlen and utf8_substr (if start, length are used)
* @param string
* @return int
* @see http://www.php.net/strspn
* @package utf8
* @subpackage strings
*/
function utf8_strspn($str, $mask, $start=null, $length=null)
{
        $mask = preg_replace('!([\\\\\\-\\]\\[/^])!', '\\\${1}', $mask);

        if ($start !== null || $length !== null)
                $str = utf8_substr($str, $start, $length);

        preg_match('/^['.$mask.']+/u', $str, $matches);

        if (isset($matches[0]))
                return utf8_strlen($matches[0]);

        return 0;
}