User blog comment:Hyp cos/R function II/@comment-5529393-20150406080531/@comment-11227630-20150406132641

{0 B 0} is indeed equivalent to {0} if B is a separator; it's equvalent to {B} if B is not a separator because we need to scan B and apply case C.

What do you mean "on the outside"? Do you mean the nested level of it is 1? (see brace notation for definition of nested level)