The CSS engine does not have a very modular boundary, because abstractions would kill the performance. It would not be very easy to use it in another browser.

The CSS engine does not have a very modular boundary, because abstractions would kill the performance. It would not be very easy to use it in another browser. However, lots of pieces of the CSS engine are modular and published as their own crates, like rust-cssparser, rust-selectors, etc. Other Servo projects are more modular; WebRender in particular just has an IPC boundary with specific messages. Servo layout would probably be more like CSS than WebRender in terms of modularity. So it's not perfect, but we're trying very hard!