Vim's Way of the Regex

vim_regex_way_rationale.txt

  NOTE: Some of Vim's way of handling certain regex features differs from
  PCRE. Some people complain about this and wonder why Vim didn't just use the
  already existing PCRE way. The reason is that Vim started getting some of
  these things at the same time Perl did, or even beforehand. So, it's not
  that Vim decided to flout history and Go Its Own Way just to be difficult.
  Respect that Vim -can- do these things and has been able to do so for a long
  time now; and suck it up and learn Vim's way. :-)