java - What is a regex "independent capturing group"?

Question

From the Java 6 Pattern documentation:

Special constructs (non-capturing)

(?:X)   X, as a non-capturing group

…

(?>X)   X, as an independent, non-capturing group

Between (?:X) and (?>X) what is the difference? What does the independent mean in this context?

Answer 1

It means that the grouping is atomic, and it throws away backtracking information for a matched group. So, this expression is possessive; it won't back off even if doing so is the only way for the regex as a whole to succeed. It's "independent" in the sense that it doesn't cooperate, via backtracking, with other elements of the regex to ensure a match.