This is PIRE, Perl Incompatible Regular Expressions library.

This library is aimed at checking a huge amount of text against
relatively many regular expressions. Roughly speaking, it can just
check whether given text maches the certain regexp, but can do it
really fast (more than 400 MB/s on our hardware is common). Even
more, multiple regexps can be combined together, giving capability
to check the text against apx.10 regexps in a single pass (and
mantaining the same speed).

Since Pire examines each character only once, without any lookaheads
or rollbacks, spending about five machine instructions per each
character, it can be used even in realtime tasks.

On the other hand, Pire has very limited functionality (compared
to other regexp libraries). Pire does not have any Perlish conditional
regexps, lookaheads & backtrackings, greedy/nongreedy matches;
neither has it any capturing facilities.