Full Idea
We are accustomed think of the actual world as the totality of facts, and so we think of any possible world as being like the actual world in settling the truth-value of every single proposition.
Gist of Idea
The actual world is a totality of facts, so we also think of possible worlds as totalities
Source
Kit Fine (Necessity and Non-Existence [2005], 02)
Book Reference
Fine,Kit: 'Modality and Tense' [OUP 2005], p.325
A Reaction
Hence it is normal to refer to a possible world as a 'maximal' set of of propositions (sentences, etc). See Idea 15069 for his proposed alternative view.
Related Idea
Idea 15069 Possible worlds may be more limited, to how things might actually turn out [Fine,K]