protected function isWhiteListed($content)
    {
        if (isset($this->functionWhitelist) === false) {
            return false;
        }

        if (\is_string($this->functionWhitelist) === true) {
            if (strpos($this->functionWhitelist, ',') !== false) {
                $this->functionWhitelist = explode(',', $this->functionWhitelist);
            } else {
                $this->functionWhitelist = (array) $this->functionWhitelist;
            }
        }

        if (\is_array($this->functionWhitelist) === true) {
            $this->functionWhitelist = array_map('strtolower', $this->functionWhitelist);
            return \in_array($content, $this->functionWhitelist, true);
        }

        return false;
    }