What does 'Script Source' refer to?

You may occasionally see Tag Assistant include the message: ‘Tag is included in an external script file’ as well as a field for ‘Script Source.’ The first notes that the Google tag is implemented inside of a separate file (such as a JavaScript file or container tag) and the second highlights exactly which file contains the Google tag. If you need to view the Google tag, you can simply click on the link in the ‘Script source’ field to see where and how the Google tag has been implemented.

Please note that these errors are dependent upon having selected the option to check external script files in the User Settings.