Note that this library is by Philip Hazel and did not originate in the Perl source code, but in Exim. Regex facilities for text processing were first implement

Note that this library is by Philip Hazel and did not originate in the Perl source code, but in Exim. Regex facilities for text processing were first implemented by Ken Thompson, long before Perl. On the topic of implementations, this is important: https://swtch.com/~rsc/regexp/regexp1.html https://swtch.com/~rsc/regexp/regexp1.html