Potential syntax incompatibility with other engines (ex: Javascript, GO, NET or POSIX) by flexible interpretation in curly brackets about pcre2

[PhilipHazel]

I always thought Perl's treatment of {,3} as a literal was an enormous gotcha, since it accepted {,3} as a qualifier. Now it treats {,3} as {0,3} which seems more reasonable. I think we should now stick with Perl compatibility but yes, add something to the docs. Anybody who cares about compatibility between engines would probably never write {,3} anyway -- they would make it clear as either {0,3} or {,3}.

[carenas]

I always thought Perl's treatment of {,3} as a literal was an enormous gotcha

FWIW, somewhat recent versions of perl (ex: 5.30) show an error instead:

% /usr/bin/perl -e 'shift =~ /x{,3}/' 'x'
Unescaped left brace in regex is illegal here in regex; marked by <-- HERE in m/x{ <-- HERE ,3}/ at -e line 1.

Anybody who cares about compatibility between engines would probably never write {,3} anyway

At least Python, Ruby and GNU RegEx seem to interpret that qualifier just like recent Perl, so I agree.

Still the fact that this is possible AND seems to match the behaviour in other engines is worth recognizing on its own:

$ perl -e 'print "$]: $1\n" if shift =~ /(x{0, 3})/' 'x{0, 3}'
5.020002: x{0, 3}
% perl -e 'print "$]: $1\n" if shift =~ /(x{0, 3})/' 'x{0, 3}'
5.036001: x

[PhilipHazel]

I have added a few words to the doc, pointing out that other engines may behave differently.