private function substr($iStart, $iLength)
{
if ($iLength < 0) {
$iLength = $this->iLength - $iStart + $iLength;
}
if ($iStart + $iLength > $this->iLength) {
$iLength = $this->iLength - $iStart;
}
$out = '';
while ($iLength > 0) {
$out .= $this->aText[$iStart];
$iStart++;
$iLength--;
}
return $out;
}