What exactly does "Types as ranges of significance of propositional functions. In modern terminology, types are domains of predicates" mean?
Update: I found in this paper (Pag 14 or 234) by Russell, where he defines what is ranges of significance, not exactly including types else propositions.
A function is said to be significant for the argument $x$ if it has a value for this argument. Thus we may say shortly $\phi x$ is significant, meaning the function $\phi$ has a value for the argument $x$. The range of significance of a function consists of all the arguments for which the function is true, together with all the arguments for which it is false.