protected function & getIntlNumberFormatter (
		$langAndLocale = NULL,
		$style = NULL,
		$pattern = NULL,
		$attributes = [],
		$textAttributes = []
	) {
		$key = implode('_', [
			'number',
			serialize(func_get_args())
		]);
		if (!isset($this->intlFormatters[$key])) {
			$formatter = \numfmt_create(
				$this->langAndLocale, $style, $pattern
			);
			foreach ($attributes as $key => $value)
				\numfmt_set_attribute($formatter, $key, $value);
			foreach ($textAttributes as $key => $value)
				\numfmt_set_text_attribute($formatter, $key, $value);
			$this->intlFormatters[$key] = & $formatter;
		}
		return $this->intlFormatters[$key];
	}