On the upside, if it's almost a superset then a data producer can make sure it is polyglot by sticking to the intersection of the two. C++ is not a strict supe

On the upside, if it's almost a superset then a data producer can make sure it is polyglot by sticking to the intersection of the two. C++ is not a strict superset of C, but the ability to include C headers is very valuable.