So much this. The UA string is flawed by itself. it shouldn't even be used anymore. The fact that browser manufacturers have to include all sorts of stuff is proof that this system doesn't work.

These strings make the parser guy in me just twitch. Do they expect many, many web developers to reliably extract accurate meaning from them?

Most developers would find and use a library rather than write their own parser. They pretty reliably extract the browser/version/platform/etc from the hundreds of thousands of UA strings you'll see in the wild.

https://github.com/tobie/ua-parser

https://github.com/browscap/browscap

A user agent parser is built in to the PHP language as well.

http://php.net/manual/en/function.get-browser.php

I think it's the other way around. This happens when a field that no-one ever defined a syntax for suddenly gets important and everyone tries to extract meaning from it using arbitrary contains() and substring() acrobatics...

So it's organic and ill-defined . . . and people are parsing it. Lovely :-)