Something I'd observe here: without expressing an opinion about PEGs vs regexes, I'd note that regexes are much more widely used. They're also completely sufficient for an awful lot of text processing tasks. PCRE regexes would be a great inclusion to the stdlib, and would probably be popular.
PEGs are a great replacement for a complicated regex, and can express a lot of things that are hard to do with a regex. But they're also more verbose, and fewer developers are familiar with their usage. PCRE regex is kind of the lingua franca of text-matching, and making it available would be helpful for newcomers imo.
