regex – Backreferences in recursions (PCRE)

In PCRE, matched groups used for backreferences before a recursion are kept in the recursion. But after the recursion they all reset to what they were before entering it. In other words, matched groups in the recursion are all forgotten.

For example:

(?J)(?(DEFINE)(\g{a}(?<a>b)\g{a}))(?<a>a)\g{a}(?1)\g{a}

matches

aaabba

if you want to reproduce, please indicate the source:
regex – Backreferences in recursions (PCRE) - CodeDay