Independent of your programming experiences, you should have learned that regular expressions are more or less write-only.

Write-only? What is he talking about!? Actually I revisited some Perl code with a relatively short reg-ex. Do you think I was able to understand what I’ve thought when I created that piece of code? Not in the slightest!

But there is a smart modifier, that enables you to comment your regular expressions: x. With /x all white-spaces are ignored and with an unescaped # the rest of the line is treated as a comment. I found a nice example, what do you think is this expression for:

No idea? Don’t even bother, I’m also stumped… Here is the solution: It’s used to check for prime numbers ;-) Using the x-mod the explanation looks much more readable (via Neil Kandalgaonkar):

So you see, it’s really helpful to use the x-modifier. At least for your own understanding :-P

A bit more explanation can be found on Perl.com.