- **NEW**: Throw `NotImplementedError` for at-rules: `page`, etc.
- **NEW**: Match nothing for `:host`, `:host()`, and `:host-context()`.
- **NEW**: Add support for `:read-write` and `:read-only`.
- **NEW**: Selector patterns can be annotated with CSS comments.
- **FIX**: `\r`, `\n`, and `\f` cannot be escaped with `\` in CSS. You must use Unicode escapes.