いつか役に立ちそうだし、メモっておく。
Railsのソースを読めてないかもしれないけど、ここで登録して参照してるっぽい。
rails/mime_types.rb at main · rails/rails · GitHub
出力結果
irb(main):002:0> Mime::SET.collect(&:to_s) => ["text/html", "text/plain", "text/javascript", "text/css", "text/calendar", "text/csv", "text/vcard", "text/vtt", "image/png", "image/jpeg", "image/gif", "image/bmp", "image/tiff", "image/svg+xml", "video/mpeg", "audio/mpeg", "audio/ogg", "audio/aac", "video/webm", "video/mp4", "font/otf", "font/ttf", "font/woff", "font/woff2", "application/xml", "application/rss+xml", "application/atom+xml", "application/x-yaml", "multipart/form-data", "application/x-www-form-urlencoded", "application/json", "application/pdf", "application/zip", "application/gzip"]
Rails APIを見てみたらrenderする時にメディアタイプを"text/calendar"にしているExampleが書かれている。