Dear boost-users, in the post http://stackoverflow.com/questions/20351369/regular-expression-cant-find-seq uence-of-numbers I discovered that if one uses an closing bracket as the first character of a character class the character class includes this bracket. This works with the standard setting of boost::regex (i.e., perl-regular expressions) but it is not documented in the manual page http://www.boost.org/doc/libs/1_55_0/libs/regex/doc/html/boost_regex/syntax/ perl_syntax.html#boost_regex.syntax.perl_syntax.character_sets Is this an undocumented feature, a bug or did I misinterpret something in the manual? The version information in version.hpp is: #define BOOST_LIB_VERSION "1_53" Info: I tried this specification of the bracket in the character set because I am used to it from emacs regular expressions. In the remainder there follows a program for reproduction of the phenomenon: #include <string> #include #include <iostream> using namespace std; int main() { std::cout << "main()\n"; string s = "98[2]00"; string exp = "^[][0-9]*$"; const boost::regex e(exp); bool isSequence = boost::regex_match(s,e); //isSequence is boolean and should be equal to 1 cout << isSequence << endl; return 0; } /** Local Variables: compile-command: "g++ -g test.cc -o test.exe -lboost_regex-mt; ./test.exe" End: */   Best regards / Mit freundlichen Grüßen Tobias Zawada Engineering / Software Development ______________________________ ITI Events We say „Thank you!“ for an outstanding ITI Symposium 2013! Make sure you save the date for next year: November 3-5, 2014 www.itisim.com ITI GmbH Schweriner Straße 1 01067 Dresden Germany T +49 (351) 26050 147 F +49 (351) 260 50 155 mailto:Zawada@itisim.com   Managing Director/Geschäftsführer Jens O. Schindler · Dr. Andreas Uhlig Commercial Register/Handelsregister Amtsgericht Dresden · HRB 2331 USt.-IdNr.: DE140297717 Diese E-Mail ist streng vertraulich und nur für den Empfänger bestimmt. Sie kann Informationen enthalten, die rechtliche, geschäftliche oder andere Vergünstigungen bedeuten. Sollten Sie nicht der ausdrückliche Empfänger sein, dürfen Sie diese Informationen nicht benutzen, veröffentlichen oder vervielfältigen. The information in this e-mail is strictly confidential, is intended solely for the addressee, and may be privileged. If you are not the intended addressee you must not disclose, print or take action based upon this transmission and should delete it from your system.