Complex sentence: The fundamental difference between context-free grammars and parsing expression grammars is that the PEG's choice operator is "ordered" (non-commutative): if the first alternative succeeds, the second alternative is ignored.
Split into simpler sentences: The fundamental difference between context-free grammars and parsing expression grammars is that the PEG's choice operator is "ordered". If the first alternative succeeds, the second alternative is ignored.