How Is COUNT-UP Implemented?

Just looked at the source of COUNT-UP and I expected to find a reference to FOR or another function to handle the details, but I only found some MAKE action!, MAKE frame! and MAKE typeset! in there.

So now wondering how this works..

SOURCE is not all that great these days, and there are reasons for that which we've discussed.

What it should be doing at minimum is pointing you to the actual source code, which is rather obvious:

count-up: redescribe [
    "Loop the body, setting a word from 1 up to the end value given"
    specialize :for [start: 1, bump: 1]

But under my proposal, FOR and COUNT-UP would basically just be synonyms.