What's the value in defining all of these constants? Do we expect developers to actually use these constants given that the difference between typing "limit_key" and `Aws\Common\Iterator\AwsResourceIterator::LIMIT_KEY` is 41 characters (66 characters if you import the class with a `use` statement)?

I don't think constants add any value for data bags like this, and even less sense for data bags that source their data from string values provided from configuration files.