Well if it works some other way, please dump it anyway and let us all know how it works?
Edit: I'm reliably informed that it's enforced at the domain level via a bloom filter stored in /System/Library/PrivateFrameworks/WebContentRestrictions.framework/WCRFilter-2025-09-29.plist
This is an opt-in feature that implements content restrictions (for e.g. parental control).