The render engine still has to do that. But that isn't much different from how it works now, where the website has to provide the necessary information.

Besides, nobody says we can't have a protocol for some additional accessibility information.

And then somebody says "how about we abstract this into some kind of markup language?" and we've come full circle.

A common markup language would be great! As long as we use it in a way that keeps us far away from compatibility problems.

But you have to make it extendable because you can't predict every possible use-case. So some kind of Extensible Markup Language, perhaps.

Maybe we make a sort of 'hyper' extension that comes with all kinds of baked in behaviours, so that we don't have to implement that behaviour ourselves when we deserialise it.

That's a good idea. Maybe we need a series of standards but all based on some kind of Standard Generalized markup.

You only get away from compatibility problems if either:

1. No-one uses it

2. There is only 1 implementation, and it is never updated