Описание тега peg
A “Parsing Expression Grammar” (“PEG”) is a formal language to describe formal languages.
A Parsing Expression Grammar (“PEG”) is a formal language that defines a set of rules to describe a certain class of formal languages similar to context-free grammars.
In comparison to context-free grammars, PEGs have the advantage of always being unambiguous, and of mapping naturally to recursive descent parsers, which makes them easy to implement.