Well, first of all, all that's necessary is the @tier array and the code generating the regex. All the rest is plumbing which I dropped in there to make sure that the regex does indeed do what it's supposed to do.

There's no Test::Block module on my machine. plan() is a function of Test::More which takes the number of tests that will be run — since I use key in scalar context (forced by the + 0), it returns the number of keys in the hash, which is the number of tests I'll be running. The %testcase hash is makes adding tests easier, and of course, if I want to test whether the regex works correctly, then I must decide ahead of time what result it is supposed to produce.

But again, nothing besides the @tier array and the code generating the regex is necessary. I just added all of the testing bits because that code wasn't easy to get right immediately, so I wanted to make sure it behaves as it is supposed to.

Makeshifts last the longest.