anchor.diff:  
   const String specGuide =
   'Everything in the curly braces can be replaced with your own value.\n'
  -'"device-id", "model-name", "os-version", "api-level" and "screem-size" '
  -'are optional.\n'
  +'"device-id", "model-name", "os-version", and "screem-size" are optional.\n'
   '"app-root" and "app-path" are required.\n'
   'An example spec would be\n'
   '''
  
positive.code:       "device-id": "HT4CWJT03204",
        "model-name": "Nexus 9",
        "os-version": "6.0",
        "api-level": "23",
        "screen-size": "xlarge",
        "app-root": "/path/to/flutter-app",
        "app-path": "/path/to/main.dart"
  
negative.code:       "device-id": "{optional}",
        "model-name": "{optional}",
        "os-version": "{optional}",
        "screen-size": "{optional}",
        "app-root": "{required}",
        "app-path": "{required}"
  