Would you please provide some notations to the code you just posted ...

I have taken a look at the discussions of the  (??{ code }) (5.8 and 5.10+) and  (?PARNO) (5.10+ only) constructs in the Extended Patterns section of perlre and I must say that while they are not ideal for a new learner of regex, they are better than anything I could provide.

Let me suggest that you (re-)read these sections thoroughly, ponder the replies to your posts above, do some (better yet, lots of) experiments, and then come back to the Monastery and post any remaining or new questions you may have. If you do all this right, you should have lots of questions because regular expressions are very powerful and can be quite subtle. Don't expect to learn it all overnight, but the effort you invest will be well rewarded.

BTW: If you have any more regex questions, be sure to mention the version of Perl you settle on using.