I find this answer from stackoverflow very clear:

https://stackoverflow.com/questions/2517050/c-construction-a nd-initialization-order-guarantees

I hope it is correct.

10) In list-initialization, every value computation and side effect of a given initializer clause is sequenced before every value computation and side effect associated with any initializer clause that follows it in the brace-enclosed comma-separated list of initializers.

Vector<int>    x { 1, 2, 3 };
Vector<String> y { "hello", "world" };

Vector x { 1, 2, 3 };
Vector y { "hello", "world" };