It’s just spring physics, hardly a slippery slope to a Newtonian physics engine let alone a relativistic or quantum physics engine. I wouldn’t describe the math as significantly more complex than Bézier curves.
Every thing you add is another step away from making building another browser engine a possibility.
I'm not absolutely certain the spring() function would be in the top 1500 of things that are hard to implement in a grassroots browser engine.
Indeed. I suspect that generally the older a web feature is, the more difficult it would be for a new browser lot implement.
The point I’m making is about the number of features. Even if every single one is simple, when most websites require a different subset, to be a viable browser, you have to implement them all so growing the number increases the difficulty of implementing a viable browser.