Very nice reading, ++.

After Perl 5.10 release I started to write a regex that parses XML, and ran into similar problems.

What I learned during crafting that expression:

• nested regexes are complicated
• They are still buggy (I found two bugs in the re engine in two days)
• There's a reason we want Perl 6 regexes/rules
• (?{print "matched so far: $&\n"}) blocks really help while debugging
• Use atomic groups wherever possible. Not only for performance reasons, but also to avoid confusing, multiple execution of embedded closures