## Intrinsic functions

    !Ref ResourceName
    { "Fn::Ref": "ResourceName" }

    !GetAtt ResourceName.AttributeName
    { "Fn::GetAtt": [ "ResourceName", "AttributeName" ] }

    !Sub "something:with:${Variable}"
    { "Fn:Sub": "something:with:${Variable}" }

    !Sub
      - something:with:${Variable}
      - { Variable: "foo" }
    { "Fn:Sub": [ "something:with:${Variable}", { "Variable": "foo" } ] }

### Syntax
| Yaml form   | Yaml Shorthand |  Original JSON        |
| ---------   | -------------- | --------------------  |
| Fn::Ref arg | !Ref arg       | { "Fn::Ref": arg }    |

Intrinsic functions can be nested, but take care with the shorthand yaml form as that cannot be nested consecutively.

Ok: `Fn::GetAZs: !Ref 'AWS::Region'`    
Not Ok: `!GetAZs !Ref 'AWS::Region'`

## Global variables
    AWS::Region
    AWS::AccountId