Multiple trailing closures

 In Swift, a trailing closure is a closure expression that is written after the function call it belongs to, rather than within the parentheses of the function call. This can make code more readable and expressive, especially for functions that take a closure as their last argument. 

Swift allows multiple trailing closures to be used with functions that take multiple closure arguments. The syntax for this is to separate the closures with commas, and write each one as a trailing closure expression.

 Here's an example of a function that takes multiple closure arguments, and how you can use trailing closures with it:

func performRequest(url: URL, completionHandler: (Data?, Error?) -> Void, progressHandler: (Double) -> Void) {
    // perform request and call completion and progress handlers as appropriate
}

let url = URL(string: "https://example.com")!

performRequest(url: url) { responseData, error in
    // handle completion
} progressHandler: { progress in
    // handle progress
}

In this example, the performRequest function takes two closure arguments: a completion handler and a progress handler. The first closure is passed as a trailing closure expression, and the second closure is passed as a labeled trailing closure expression, using the syntax progressHandler: { ... }.