[jdd]

Benchmark.js (http://benchmarkjs.com), which jsPerf uses, does checks the UA string as well as feature tests for various environments. You can check the code out at https://github.com/mathiasbynens/benchmark.js/blob/master/be....

Here is a MSDN post that examines some of the platform tokens http://msdn.microsoft.com/en-us/library/ms537503(VS.85).aspx