Full Idea
The strategem of talk about possible worlds is that truth assignments of sentences and extensions of predicates may vary, but individual names don't alter their reference (unless they don't refer). They are a neutral peg for descriptions.
Gist of Idea
In possible worlds, names are just neutral unvarying pegs for truths and predicates
Source
Ruth Barcan Marcus (Essential Attribution [1971], p.194)
Book Reference
-: 'Nous' [-], p.194