private function processLeadingIndentationTags ($sMessage)
    {
        $bTagFound = true;
        while ($bTagFound && strlen($sMessage) > 0) {
            if (substr($sMessage, 0, $this->iIndentTagLength) == $this->aConfig['indent_tag']) {
                $this->iIndentationLevel++;
                $sMessage = substr($sMessage, $this->iIndentTagLength);
            } elseif (substr($sMessage, 0, $this->iUnindentTagLength) == $this->aConfig['unindent_tag']) {
                $this->iIndentationLevel = max(0, $this->iIndentationLevel-1);
                $sMessage = substr($sMessage, $this->iUnindentTagLength);
            } else {
                $bTagFound = false;
            }
        }
        return $sMessage;
    }