Exploring Coroutines in PHP

Just to clarify my intent with posts like this:

I'm not suggesting that PHP is the ideal tool for every use case. The goal is to share a concept that might be unfamiliar to some developers, using PHP as the context.

Sometimes learning about a concept in a familiar language helps you recognise where it might be useful elsewhere or apply it in a language that supports it better.

Terms like coroutines, concurrency, promises, etc, can be confusing; I just like to demystify them with easy-to-grasp examples. That does mean that examples can be contrived or very simple, but they are designed to get the point across.

Thanks for all the comments so far!