フォロー
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$ curl --head https://www.nicovideo.jp/user/1/video?rss=2.0
HTTP/1.1 200 OK
...
Content-Type: application/rss+xml; charset=utf-8
$ curl --header "Accept: application/rss+xml" https://www.nicovideo.jp/user/1/video?rss=2.0
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>406 Not Acceptable</title>
</head><body>
<h1>Not Acceptable</h1>
