32 Regular expressions library [re]

32.4 Namespace std​::​regex_­constants [re.const]

32.4.1 General [re.const.general]

The namespace std​::​regex_­constants holds symbolic constants used by the regular expression library.
This namespace provides three types, syntax_­option_­type, match_­flag_­type, and error_­type, along with several constants of these types.