As the annotation references to exactly one expression. There is only one type expression possible

All notations are PascalCase

PascalCase with a starting uppercase letter. This is also in other languages a known convention for types or classes

Types MUST be chosen from the existing list

see primitives

Operators MUST be chosen from the existing list

see operators

explicit AttrSet and List keywords are PROHIBITED

See the correct usage here

complex types MUST include their members explicitly

There is no AttrSet and no List keyword.

explicit Any is PROHIBITED

Correct usage with type variables see here

Allowing arbitrary values within complex-types

It is possible to allow arbitrary values within complex types, but it requires an explicit statement.

There is no implicit any.

Type variables must be written in LOWERCASE to prevent confusion

They are used instead of the Any Keyword.

For Type bindings it is PROHIBITED to choose names from the reserved list

This will help to keep the code clean. Reduces complexity, resolves for shadowing and namespace conflicts, with global names.