title: Why does GetAttr not work on cloudformation template parameters?
body: <p>Have a collection of cloudformation templates in a parent-child relationship and want to pass an AWS::IAM::Role into the parameters of a child stack and use GetAttr to get the Arn.</p>
  
  <p>This fails validation because can only call GetAttr on resources, not on parameters. </p>
  
  <p>Anyone know/guess why this is designed in this way? </p>
  
  <p>It's not a problem as it can be worked around by just passing the Arn into the stack, I'm just curious really</p>