Why does \R behave differently in regular expressions between Java 8 and Java 9?

Question

The following code compiles in both Java 8 & 9, but behaves differently.

class Simple {
    static String sample = \         


        

Answer 1

It was a bug in Java 8 and it got fixed: JDK-8176029 : "Linebreak matcher is not equivalent to the pattern as stated in javadoc".

Also see: Java-8 regex negative lookbehind with `\R`