public function mergeGlobals(array $context)
    {
        // we don't use array_merge as the context being generally
        // bigger than globals, this code is faster.
        foreach ($this->getGlobals() as $key => $value) {
            if (!array_key_exists($key, $context)) {
                $context[$key] = $value;
            }
        }

        return $context;
    }