Why "Cannot find type 'TextOutputFormat' in scope" when this type is from the stdlib?

I'm trying to add syntax highlighting to MarkdownUI. This uses Splash.

Adding some sample code and get this compile error:

But TextOutputFormat is from the Standard Library.

TextOutputFormat isn’t in the standard library. Can you find some documentation or an article that mentions it, to point us to what you’re looking for?

Nevermind, I search "swift TextOutputFormat" and got TextOutputStream.

So where is TextOutputFormat? Must be something in the Splash package?

Here: TextOutputStream | Apple Developer Documentation

This compile:

import Foundation

struct ASCIILogger: TextOutputStream {
    mutating func write(_ string: String) {
        let ascii = string.unicodeScalars.lazy.map { scalar in
            scalar == "\n"
              ? "\n"
              : scalar.escaped(asASCII: true)
        print(ascii.joined(separator: ""), terminator: "")

I have no idea what TextOutputFormat you’re talking about. That’s why I asked for a link to an article, to see if the article would make it more clear where it comes from or what was intended.

I found it. It's part of the Demo of MarkdownUI code syntax highlighting using Splash.

Just clone it, there is a Demo app Xcode project. Open it and TextOutputFormat is an implement of protocol Splash.OutputFormat