>>42
一部誤っていたので訂正。

6.5.16 Assignment operators

3
An assignment operator stores a value in the object designated by the left operand.
An assignment expression has the value of the left operand after the assignment, but is not an lvalue.
The type of an assignment expression is the type the left operand would have after lvalue conversion.
The side effect of updating the stored value of the left operand is sequenced after the value computations of the left and right operands.
The evaluations of the operands are unsequenced.

なので代入式の値は「左辺式(left operand)に右辺式(right operand)の値を代入した後の値を右辺値(rvalueの意味)として評価した値」が正しかった。