Idiom #369 makes no sense?

[Bart-B]

Idiom #369 Parse matching brackets

None of the provided wiki links seem to have any bearing on the given task.
At last I could not find any refernce to what it is supposed to do.
The expected output seems to have no logical relation to the given input.
(Well, I'm not a mathematicion or anything the like, so I may very well be totally wrong)
(And, the issue tracker may not be the right place to complain about this, but I saw no other way. It seems to be the only way to contact you)