[andrewaylett]

I am, I'm sorry to say, unconvinced. I'm not keen on 'magic' behaviours like auto-converting of values to arrays -- while the behaviour of the document may be well specified globally, it's nice to be able to see what something's going to do based on immediate (or even no) context.

What I'm very much liking at the moment is the way Dropwizard uses Jackson's YAML (and by extension, JSON) parsing for configuration -- your configuration file maps 1-1 to a class in your application, and Jackson is configured to fail if you're either missing a field that's not marked as optional or you've got extra fields in your YAML that don't map to anything. Type-safety FTW!

On the subject of wanting to refer to earlier bits of configuration: if you need to use one value as part of another, your configuration system might not be exposing the right level of detail. Of course, you might not be able to change that.