Comment 1 for bug 1414362

thanks for the example.

the regex implementation provider was changed between versions 0.843 and 0.850 from boost <http://www.boost.org/doc/libs/1_57_0/libs/regex/doc/html/index.html> to libstdc++ <https://gcc.gnu.org/wiki/Regex>. hopefully tweaks can be found; otherwise we can always revert to the boost implementation.

2 sides to this topic:
- validity. the first step would be to make sure the example expression is actually valid (starting with a "?" sign seems strange to me); and if it is, why libstdc++ rejects it.
- performance.