regex
This version has 20 feature flags, 17 of them enabled by default.
default
std
perf
unicode
perf-cache
perf-dfa
perf-inline
perf-literal
unicode-age
unicode-bool
unicode-case
unicode-gencat
unicode-perl
unicode-script
unicode-segment
aho-corasick
memchr
unstable
use_std
pattern