detect browser from user agent
Picking out the right browser from a User-Agent string takes more than searching for a name: Chrome, Edge and Opera all share the Blink engine and carry similar tokens in the same string, so the order each pattern is tested in decides the outcome. This page details that order and where it usually breaks.
The Windows NT 10.0 to "10/11" mapping exists because the two versions share the same NT build number, the string alone does not tell them apart.
The string contains Chrome/120.0.0.0 and Edg/120.0.0.0 at the same time; the Edg/ token has to be checked first, otherwise the result comes out as Chrome.
The 17 comes from the Version/17.0 token, not the number after Safari/, which here is the WebKit build, not the browser version.
It is an HTTP header sent by the browser with every request, in the format: "BrowserName/Version (OS; Architecture) Compatibility/1.0 Engine/Version". The syntax is defined by RFC 7231 and was originally created so servers could adapt responses for different clients.
Yes, if the parser checks the wrong token first. Both include Chrome/version in the string, inherited from Chromium, but only Edge also includes Edg/version (with a single g, to avoid colliding with old rules for the EdgeHTML-based Edge). A correct parser looks for Edg/ before treating the string as plain Chrome.
The format is major.minor.build.patch. Since Chrome adopted that scheme, the minor and build fields stay pinned at zero in most stable releases, and only the major number and the patch change between versions, so a string ending in .0.0 is the norm, not a parsing mistake.
Yes. Brave, for instance, deliberately sends the exact same User-Agent as Chrome with no brand of its own, to keep sites from treating it differently or using the browser name as an extra fingerprinting signal; the only real way to identify it is through the Sec-CH-UA client hint or the navigator.brave API, not the string.