what does this convoluted regex do

what does this convoluted regex do

References

Reference NO 1

http://stackoverflow.com/questions/13656656/what-does-this-convoluted-regex-do

Reference NO 2

http://pshort.us/wp/blog/2012/08/26/why-regular-expressions-does-not-exist-tests-are-convoluted/

Reference NO 3

https://xkcd.com/208/

Reference NO 4

http://davidcel.is/blog/2012/09/06/stop-validating-email-addresses-with-regex/

Reference NO 5

http://cs.stackexchange.com/questions/9132/what-is-meant-by-give-pattern-of-a-regular-expression

Reference NO 6

http://superuser.com/questions/312073/use-notepad-to-change-under-score-case-to-camelcase

Reference NO 7

http://ayende.com/blog/4005/challenge-the-regex-that-doesnt-match

Reference NO 8

http://www.perlmonks.org/?node_id=989705