please add tests for the new code as well

Sorry for disagreeing but exactly why?
I understand the importance of tests but there are already 22 test values supposed to be valid and 5 supposed to be invalid.
Yes, of course, I can think of a few more but especially when comparing to other methods that have less tests I think 22 valid & 5 invalid is more than solid enough.

So why should there be more?
The format remains the same as my PR doesn't even touch the format and structure validation but only updates the available area/district codes.

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But thanks for commenting. I had another look at the regex and there is one obsolete | operator. Will fix in the next hour.