see sibling comment for specific detials. From a explanatory pov: I suspect you're thinking that the mutable text state should be "core" but it's actually not

see sibling comment for specific detials. From a explanatory pov: I suspect you're thinking that the mutable text state should be "core" but it's actually not, it's part of the "shell". Think about a RESTful frontend providing UI to a (mutable) database holding the state, the database conceptually is the "core" of the program, but in parlance of the architectures discussed here it would be in the "shell". It is a bit confusing, unfortunately, and it's one of the things I dislike about this classification scheme.