At the beginning of Chapter 8 of Kubilius's Probabilistic Methods in the Theory of Numbers, the author defines $Q=Q(E)$ to be a completely additive nonnegative function defined for all Borel subsets $E$ of $\Bbb R^n$ (that is, some kind of measure defined on the Borel subsets of $\Bbb R^n$). The author then uses the terminology that $I$ can be an "interval of continuity" of the function $Q(E)$ (nothing more is said about what $I$ is).
What is the precise definition of "interval of continuity" in this context? Where can I find that definition?
This question was first posted on Mathematics Stack Exchange, but it didn't receive any answers for over a week. One comment made me wonder whether an interval of continuity might be a set of the form $I_1\times\cdots\times I_n$, where each $I_j$ is an interval in $\Bbb R$, such that $Q(\partial I)=0$ where $\partial I$ is the boundary of $I$; but I don't trust this hunch enough to use it without confirmation.
(Kubilius is actually talking there about Borel subsets not containing the origin, but I'm pretty sure that's irrelevant to my question.)
