I just looked at https://tc39.es/ecma262/#sec-notational-conventions and noticed that they have been using an extended grammar notation (based on
the one used by K&R in The C Programming Language) for some years now.

It's not quite a VW-grammar yet, but I presume they introduced it because
the language now has so many weird corners, where a general version of a production cannot be used without causing problems.

Productions can be parametrized with [Word1,Word2,...], such that a rule Nonterminal[Alfa,Beta] is defines three rules, for Nonterminal, Nonterminal_Alfa and Nonterminal_Beta. RHS Nonterminals can be
parametrized in various ways as well. NT[+Alfa], NT[~Alfa], NT[?Alfa]
with various meanings.

Are there any parser generators out there that support these "features"?

/Lasse

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