Artifact is simply named after what it does: it is a way to write and track your [artifacts](https://en.wikipedia.org/wiki/Artifact_(software_development)
The partof attribute is much more powerful than a simple list. You can do:
[SPC-name]
partof = "REQ-[name, other, nested-[more, link]]"
Which is equivalent to:
[SPC-name]
partof = "REQ-name, REQ-other, REQ-nested-more, REQ-nested-link"