DataSift makes use of the Google RE2 regular expression engine. This has a subtly different syntax in some cases and a slightly different function set to the PCRE library which is the most common.
The RE2 engine omits some features:
- most VIM-specific repetition commands
- no possessive repetitions
- some grouping formatting (see details below)
- several empty string selectors, including all VIM-specific ones
- backreferencing escape sequences
- Perl-style spacing character classes
- all VIM-specific flags and most VIM-specific character classes
For the full differences between PCRE and RE2, check out the syntax page on Google Code.
Make sure you've read our page on special characters.