[Adopted as a DR at the November, 2019 meeting.]

According to 7.6.19 [expr.assign] paragraph 3,

If the left operand is not of class type, the expression is implicitly converted (7.3 [conv]) to the cv-unqualified type of the left operand.

Since the second operand of an assignment operator can now be an initializer-clause, the referent of “expression” is unclear.

See also issue 1542.