That User-Agent isn't really valid. It's the "like Gecko". If you only read the BNF, then okay, it's valid. But the various sections are supposed to have seman

That User-Agent isn't really valid. It's the "like Gecko". If you only read the BNF, then okay, it's valid. But the various sections are supposed to have semantic meaning — they're supposed to be products with optional versions and comments. Like, Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv 11.0) Means the product "Mozilla" with version "5.0", followed by a comment of "Windows NT 6.3; Trident/7.0; rv 11.0". Thus their UA of… Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv 11.0) like Gecko …includes the products "Mozilla", "like" and "Gecko". Like the article mentions, "like Gecko" has been done before: > Safari was the first browser to add “like Gecko” so that anyone sniffing for “Gecko” in the user-agent string would allow the browser through. And they put it in a comment, not as two separate products: > AppleWebKit/536.26 (KHTML, like Gecko) See http://www.ietf.org/rfc/rfc2616.txt http://www.ietf.org/rfc/rfc2616.txt.