As of P0400R0 (Wording for Order of Evaluation of Function Arguments), we have in subclause 7.6.1.3 [expr.call] paragraph 8:

The postfix-expression is sequenced before each expression in the expression-list and any default argument. The initialization of a parameter, including every associated value computation and side effect, is indeterminately sequenced with respect to that of any other parameter.

What about the case when the element in the expression-list is a braced-init-list rather than an expression? The braced-init-list is certainly evaluated left-to-right, but is that required to happen after we evaluate the postfix-expression?