Java-8 regex negative lookbehind with `\R`

Question

While answering another question, I wrote a regex to match all whitespace up to and including at most one newline. I did this using negative lookbehind for the \\R

Answer 1

The construct \R is a macro that surrounds the sub expressions into an atomic group (?> parts ).

That's why it won't break them apart.

A note: If Java accepts fixed alternations in a lookbehind, using \R is ok, but if the engine doesn't, this would throw an exception.