Good day.
Some time ago we discuss that a quantified assertions can be used: https://lists.exim.org/lurker/message/20110502.103121.96e51b9d.en.html Here is pcretest listing: PCRE2 version 10.31 2018-02-12 /(?<=(?=.)?)/ Failed: error 125 at offset 0: lookbehind assertion is not fixed length ab Assertion have a fixed 0 length not matter it quantified or not. So such patterns shouldn't rise error. It seems it's no error in Perl. --## List details at https://lists.exim.org/mailman/listinfo/pcre-dev
