Nexus guide clarifications needed

Hello,

In Nexus guide, I see a sentence which goes as follows: Nexus roles, events, and artifacts inherit the purpose and intent attributes of the corresponding Scrum roles, events, and artifacts, as documented in the Scrum Guide. However, my questions are as follows:

1. In Scrum guide, refinement is not a mandatory event, its an optional one. Whereas, in Nexus, Refinement is a mandatory event

2. In Scrum guide, Sprint goal is not a artifact. Whereas, in Nexus, Nexus goal is an artifact.