It’s coming from [here](https://github.com/rubygems/gems/blob/8a83212b23abf87d1a7620870018a1d7749f7c9c/lib/gems/configuration.rb#L17), but I agree, it's a little confusing. Perhaps too much [meta-programming magic](https://github.com/rubygems/gems/blob/8a83212b23abf87d1a7620870018a1d7749f7c9c/lib/gems/configuration.rb#L40)?