Re: JSON parser grammar

My inclination would be to require ES5 implementation to exactly conform the whatever JSON grammar we provide and to throw syntax errors if the input doesn't exactly conform to the grammar. (in other say that the section 16 extension allowance doesn't apply to JSON.parse.  If an implementation wants to support JSON syntax extensions it could always do so by providing a JSON.parseExtended function (or whatever they want to call it) that uses an implementation defined grammar.