What is it?
The ability to perform string matching seems like a useful, or even essential skill, but the expression is too complicated.
Wasn't there a clearer way to write it? Well, I'll remember.
The most important thing to remember is that regular expressions can be used to ask questions such as "Is this the correct format for a zip code? or "Is the format of the email address correct? and "Is it correct as a ZIP code format?