Unrecognized PCRE extended construction

[artelse]

When try to convert this common regex:
(rxt-pcre-to-elisp "^(?:ISBN(?:-1[03])?:? )?(?=[0-9X]{10}$|(?=(?:[0-9]+[- ]){3})[- 0-9X]{13}$|97[89][0-9]{10}$|(?=(?:[0-9]+[- ]){4})[- 0-9]{17}$)(?:97[89][- ]?)?[0-9]{1,5}[- ]?[0-9]+[- ]?[0-9]+[- ]?[0-9X]$")
The debugger reports:

Debugger entered--Lisp error: (rxt-invalid-regexp "Unrecognized PCRE extended construction `(?='")
  signal(rxt-invalid-regexp ("Unrecognized PCRE extended construction `(?='"))
  rxt-error("Unrecognized PCRE extended construction `(?%c'" 61)

Is this one of the PCRE limitations?

[LemonBreezes]

When try to convert this common regex: (rxt-pcre-to-elisp "^(?:ISBN(?:-1[03])?:? )?(?=[0-9X]{10}$|(?=(?:[0-9]+[- ]){3})[- 0-9X]{13}$|97[89][0-9]{10}$|(?=(?:[0-9]+[- ]){4})[- 0-9]{17}$)(?:97[89][- ]?)?[0-9]{1,5}[- ]?[0-9]+[- ]?[0-9]+[- ]?[0-9X]$") The debugger reports:

Debugger entered--Lisp error: (rxt-invalid-regexp "Unrecognized PCRE extended construction `(?='")
  signal(rxt-invalid-regexp ("Unrecognized PCRE extended construction `(?='"))
  rxt-error("Unrecognized PCRE extended construction `(?%c'" 61)

Is this one of the PCRE limitations?

Hello artelse. I am currently working on a fork of pcre2el. What exactly is the (?= construction supposed to do? It would be nice if you could link documentation. I might be able to fix this. Ideally, there will be a mapping of ?= to some rx operator.

[artelse]

Hi, I took that regex from the Regular Expressions Cookbook chapter 4.13 of which an online version is here: https://www.oreilly.com/library/view/regular-expressions-cookbook/9780596802837/ch04s13.html
In the mean time constructed a regex that works for me, but it would be great if pcre2el would cover these constructs.

[gvol]

It's a positive lookahead assertion: http://www.pcre.org/current/doc/html/pcre2syntax.html#SEC19