A way around "multi-level classification"

[2colours]

A sister issue of https://github.com/Raku/doc/issues/4293.

The capability of multi-level classification is nice but sometimes, it would be good to really just use an Iterable as a key of a flat Hash. It seems too broad to lose all control of the otherwise default behavior by introducing Iterables in the classification.

[2colours]

A couple of ideas:

• an "adverb" to control multi-level classification; either opt-in or opt-out
• draw a distinction using containers (or conceptually rather itemization)
• draw a distinction using Slips