Seems like a riff on the famous Perl Compatible Regular Expressions library (http://www.pcre.org), which is used in a bunch of high-profile things (PHP, and Apache Server, for starters). Kind of like "less" vs "more".

So a bit of an inside joke I guess, but most people familiar with regexes will probably have heard of PCRE, so it's not a terribly obscure reference. I liked it :)