One of the “chunks” in the blorb spec is the RIdx, which lists resources by number. In that section of the spec, it says:
For example, when a Z-code game calls @draw_picture with an argument of 3, the interpreter would find the index entry whose usage is ‘Pict’ and whose number is 3.
There are four types of resources (pict, snd, data, exec). Can there be a pict with number 3 AND a sound with number 3? I’ve scanned a few gblorb files from the if archive at random, and it looks like all numbers are unique. But the way this is worded – find entry with (Pict && 3) – makes it sound like each resource type can have its own set of numbers.