[ianbicking]

I think there's a lot of value to thinking things through before into a relatively formal thing like this; like probably this is already a second system... the first probably being bespoke codegen tools or something, as the docs seem to be from people who have spent some real time struggling with existing tools.

When you are doing a second system you've already experienced the architecture you get when you explore by the seat of your pants. You've built some intuition, but you've hit the point when you need larger and more formal plans.

In this case the designer may not have previously even wanted or considered writing a programming language, but realized the generality and complexity of their ambitions required the very formalism of a programming language, and then that the plan was a real part of the finished product.