New category permission - "cannot see"/"exclude"

Guys - can you sanity-check this please?

I think I might of thought of a way of aheiving something like this based on existing functionality.

Lets say I want to keep any topics that are tagged “secret” non-visible to a certain group.

Is it not as simple as changing the group’s settings so that any topics tagged “secret” are muted for group members?

Likewise if I want to a keep a category non-visible to a certain group, is it not as simple as changing the group’s settings so that any topics in that category are muted for group members? (and also installing the Hide Muted Categories theme component)?

Also - I can’t find any documentation describing how the Discourse muting functionality works - can anyone help?