CSS definition syntax

CSS is one of the few languages that uses its own language for syntax description — definition syntax. This "language" is used in all CSS specifications. "So what?" — you thought, — "I'm don't read specs anyway, I know CSS without it". It might be true, but Custom Properties came into our life not so long ago. Later it turned out that we needed to describe their value syntax somehow, otherwise an animation will not work. And what was decided to use for this? Definition syntax! Also, CSS Houdini is coming. You can use Paint Worklet already (some browsers supported it), that takes parameters which value syntax is describing in definition syntax (its subset, but still).

Definition syntax is coming from specs to the code. And knowing it for sure will not be superfluous. How does it works, what tools we have for it? This talk is about it, as usual with deep dive into technical details and interesting architectural solutions.