XML namespaces do offer some nice possibilities. But the lack of official JSON namespaces doesn't prevent you from doing something like: { "built_i

XML namespaces do offer some nice possibilities. But the lack of official JSON namespaces doesn't prevent you from doing something like: { "built_in": "value", "org.example.my_extension": "value" } If you want to validate it, you might need to jump through some JSON schema hoops, of course.