Xcode 10 code completion placeholders — what is the "T"?

In Xcode 10 code completion, the text underlying the placeholder tokens has an extra #T# before it (to see that this is so, copy and paste the inserted code template into a different text editor):

let alert = UIAlertController(    title: <#T##String?#>, message: <#T##String?#>,     preferredStyle: <#T##UIAlertController.Style#>)

What is that? Does "T" mean Type? What difference does it make in my usage of the placeholder?