Architecture: what counts as public contract

Why the line between the public API and the visible internals falls where it does. What is public, and what is only visible, is in architecture.md.

The reason is not the prefix

Below WebFunction.return_parser and WebFunctions.forms lies the resolution machinery itself, in nodes whose names do start with _, and none of it, visible or private, is needed in order to declare a function, mount it or call it, which is what the contract undertakes to cover. A ReturnParser is not even built from outside (its root compiles the Download marks into those private nodes), so promising it stable would mean promising the shape of its machinery.