RunLoop.main or DispatchQueue.main when using Combine scheduler?

Using Swift
5

Thanks, now I have a better understanding whether to use RunLoop or DispatchQueue as Scheduler.

I was wondering how people would be able to learn this from the documentation? (Choosing Dispatch Queue or RunLoop)
And It seems like neither extension DispatchQueue: Scheduler { ... } nor protocol Scheduler { ... } mentions about the serial queue requirement for Combine's operators.

I tried to use a concurrent queue as the scheduler but there is no warning in the console or crash to help programmers avoid this.

let concurrentQueue = DispatchQueue(label: "ConcurrentQueue", qos: .default, attributes: .concurrent)

Just(10)
    .subscribe(on: concurrentQueue)
    .map { "\($0)" }
    .receive(on: RunLoop.main)
    .sink { value in print(value) }
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