SMOP Prelude Lexical Scope

Differently from Perl 5, in Perl 6 packages are not always global. The lookup for a particular package name always traverses the lexical scope hierarchy (unless explicitly with the GLOBAL package upfront (or its synonym "*"). The same happens for every Perl 6 operator.

This means that on the top of the scope hierarchy there should be a special scope, that will be the ultimate root of every lexical scope and will provide the "Perl 6 Prelude" as symbols that can be subject to lexical lookup.

What does the Prelude Lexical Scope define?