>HSS is a language based on CSS, but offers many more advanced features, such as object orientation, rule nesting, expressions, references to other objects, modularization (code reuse), etc.

Ew. This is an advertisement? Elegance is usually achieved when you hit a maximum of capabilities with a minimum of explicitly defined features. The last thing you want is so many different constructs that when someone reads your code they have to keep a reference manual handy.

Granted, I haven't worked my way through the spec, but maybe there's a better way to phrase that sentence that doesn't evoke memories of C++.