90s-late 00s cars are actually on repairability in my experience, because they already have computers which help you diagnose failures easily with a $20 OBD2 scanner (this saved my ass a couple of times, when I could almost immediately see the error whenever my car died, fiddle or re-plug the wiring of the failed component and keep going), and they don’t yet have all the over-complicated, designed-to-fail, hard-to-reach crap that a lot of new cars have.
So, here’s my attempt
The first portion (
^.?$
) matches all lines of 0 or 1 characters.The second portion (
^(..+?)\1+$
) is more complicated:(..+?)
is a capture group that matches the first character in any line, followed by a smallest possible non-zero number of characters such that (2) still matches (note that the minimum length of this match is 2)\1+
matches as many as possible (and more than 0) repeats of the (1) groupI think what this does is match any line consisting of a single character with the length
1
(due to the note in (1), so that the repeating portion has to be at least 2 characters long), orTherefore, combined with the first portion, it matches all lines of the same character whose lengths are composite (non-prime) numbers? (it will also match any line of length 1, and all lines consisting of the same string repeated more than one time)