[girvo]

Parsing expression grammars (pegs) are usually IME more maintainable long term, partially just because of much more testable and composable they are

[afiori]

I suspect but am not sure that PEGs cannot do negative nor positive lookbehind, but it is not a very used feature.

[girvo]

Yeah that’s true IIRC but it’s rarely been a problem for my usage!