protected function evalKeyLabel($key)
    {
        if ($this->variablePrefix === true) {
            $output = '{{ <span>%s</span> }}';
        }
        elseif (is_array($this->variablePrefix)) {
            $prefix = implode('.', $this->variablePrefix);
            $output = '{{ <span>'.$prefix.'.%s</span> }}';
        }
        elseif ($this->variablePrefix) {
            $output = '{{ <span>'.$this->variablePrefix.'.%s</span> }}';
        }
        else {
            $output = '%s';
        }

        return sprintf($output, $key);
    }