Why will this recursive regex only match when a character repeats 2^n - 1 times?

Question

After reading polygenelubricants\'s series of articles on advanced regular expressions techniques (particularly How does this Java regex detect palindromes?), I decided to a

Answer 1

In case you would like a fully functional PCRE expression to match palindromes, you can use the following:

/^(?:(.)(?=.*(\1(?(2)\2))$))*+.?\2?$/