After I wrote Fizzler in a burst of development enthusiasm a few months back, it's been sat on Google Code - a solution in need of a problem to solve. That is until Colin Eberhardt emailed me to report a bug in the selector engine, and to talk a bit about the way he was using Fizzler when working with WPF. This was totally outside the domain I'd anticipated Fizzler being use in, and Colin E has now revealed his project in full. By wrapping part of Fizzler in a few interfaces, thus abstracting it away from HTML and towards a more general purpose solution, he was able to use it to query a XAML UI definition and apply style declarations. CSS selectors for WPF!
This is an amazing use case for a library which I hope will start to see more use in the future. Thanks to Colin E for letting me know about the work which Scottlogic are doing with Fizzler.