What regex syntax does Sublime Text use? POSIX? POSIX Extended?
Sublime Text's Find and Replace functions, along with snippets, are powered by Boost's pcre (Perl-Compatible Regular Expressions) engine. For syntax highlighting, Sublime Text 3 and 4 use a custom oniguruma-compatible engine, with fallback to Oniguruma itself, for .sublime-syntax files. Oniguruma is used for the older tmLanguage format, and was the only engine used for syntax highlighting in Sublime Text 2.