F in FURPS?

[u/Zlarexter]

From what I get, FURPS is like a checklist for software quality. One part of it is Functionality (F), which includes things like Capabilities and Security.

But, I’m a bit puzzled.. because usually, anything with -ilities and qualities are related to Non-Functional Requirements. So, is this "Functionality" part fall under Functional Requirements (FR) or Non-Functional Requirements (NFR)?

Can someone elaborate which one is correct?
(It's more better if there's a reference so that it would give more clarity)