Thank you Gay for posting.
I noticed an unfamiliar entity that is created by the Interpreter. Its InputForm is:
Entity["Food", {EntityProperty["Food", "FoodType"] -> ContainsExactly[{
Entity["FoodType", "Elderberry"]}],
EntityProperty["Food", "AddedFoodTypes"] -> ContainsExactly[{}]}]
What kind of entity is this?
I suspect it's a compound Entity given the "plus" sign and its own icon.
The closest example I can find is in the first example in the "Scope" section in https://reference.wolfram.com/language/ref/Entity.html .
However the syntax is about the first argument, not the second argument.