I hate to look a gift horse in the mouth but I think I'd expect this to simply be a property; a get/set at most to also support the backing `content.contentConstructor` convention you're establishing, while otherwise promoting simply setting the constructor function e.g. Object, Person, etc.

If nothing else that gives a pretty clear way to check for homogeneity of the content, though I'm not sure if that's the responsibility of the rangeController in consideration of the grander data plan.

Also it should be pretty easy to set in simple cases. Which reminds me, @PierreFrisch I think the blueprint may be missing a function valueType…