The Standards Document 1.1 says this about the stack:
The absolute minimum standard for stack size is defined as:
let the ‘usage’ of a routine call be 4 plus the number of local variables it has. During a game the total of the usages for each routine in the recursive chain of routines being called, plus the game’s own stack usage, can be assumed to never reach 1024.
I find the usage of “the stack” in this section of the doc to be a little ambiguous. I’m assuming it’s referring to what Quetzal would term the per-call “evaluation stack”?
I’m not clear on how the “usage” of 4 (words?) is arrived at. It matches what’s set aside in Quetzal, but I can’t find a definition in the standard stating what it intends those 4 words to be used for. Is it meant to be left for the implementer to decide?