I don't know if this is the intend of Tom, but I was also stumbling on this issue and the only reasonable explanation I can come up with is that: One key can't

I don't know if this is the intend of Tom, but I was also stumbling on this issue and the only reasonable explanation I can come up with is that: One key can't have multiple values with different types. For example in json: { "name" : { "first" : "Bob", "last" : "Smith" } } How would you add a "alternative" key to the "first" value type. The only way i can think of is something like this. { "name" : { "first" : "Bob", "first.alternative": "Robert", "last" : "Smith" } } or as @latk suggested, let "first" be an array, with it's first entry being the non alternatives. { "name" : { "first" : ["Bob", "Robert"], "last" : "Smith" } } I think this is by design. To quote @mojombo "simple configuration file that maps unambiguously to a hash table". But this is only a guess.