Thank you for your thoughtful answer, it's clarified some issues. I'm afraid it also raises more questions for me (I probably need to go study CoffeeScript some more). BTW, the text I added is actually from the first example - the simplest:

  await $.getJSON url, defer json

Is the following right? Syntactically, "defer json" is an argument to the function "$.getJSON". So you could write it like this:

  await $.getJSON( url, defer(json) )

The code we are waiting for is the "$.getJSON" call. That code indicates that it is finished by calling the function returned by defer.

But what does the function returned by defer do? It looks like it (somehow) sets its argument to the result... so in the above example, "json" (somehow) gets the result of the call; in your example, "x" (somehow) gets a value. I'm guessing it's some convenient compiler magic that ICS does, and not an issue of CoffeeScript syntax.

An upshot of this is you can't give defer any old argument (e.g. a numerical value) - it has to be a variable that is capable of being set.

Also, who is the "callee"? A "callee" is a function that is called... Oh, does it mean (eg) "$.getJSON" is a callee, and it calls the callback function given to it (in the jQuery docs, it's notated as "success(data, textStatus, jqXHR)"; here, that success function is the function returned by defer). I guess, given the purpose of ICS, there will always be a callee in the block - but it seems to me that, syntactically, you could just directly call the function returned by defer. Ah... but (I bet) part of the compiler magic is that you are only allowed to call the function returned by defer from within another function - this is because the result of that other function is needed in order to set the argument of defer to it. Whew.

One last thing: the description talks about "deferrals" begin "fulfilled", but it doesn't say where these defarrals come from. Now, I think they are created by calling defer.

Hmmm.... it's probably better for me to think about this in terms of lisp macros, instead of C calls, as macros allow you to do weird source code transformations, like setting the value of a variable given as an "argument". i.e. ICS is a macro.