A further thought on this: at one stage @hostilefork suggested (| Synthetic |) [[Asymmetric]] {> Delimiters <}. Might we be able to resurrect this as a tool for including literal GROUP!s in a COMPOSE? The syntax even makes intuitive sense — conceptually, COMPOSE gets rid of the outer layer of brackets, leaving the inner layer.
So, if that idea works out, we could get rid of any special ‘UNUSE specifiers’, since it would let us just do this:
do compose/deep [
let one: (char)
let two: [repeat 2 (char)]
parse (string) [comment "your code here" ((do unuse [one two] (rule)))]
]