Disable this!

position: is simply indicating what the parameter name is.

This happens when you declare a function using the underscore in place of a public parameter name as shown below. AppCode is showing you what the function's internal parameter name is. I generally find this feature useful, but if you want to disable it, poke around in the settings for something similar to "Inline parameter hints".

func testFunc(_ firstParam: String?, _ testParam: String?) -> String? {
    return nil
}