[1] Tk - HTTP | MDN (2016-12-13 18:16:29 +09:00) https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Tk
[2] Tracking Preference Expression (DNT) (2019-01-16 01:50:48 +09:00) https://www.w3.org/TR/2019/NOTE-tracking-dnt-20190117/#x7-3-tk-header-field-for-http-responses