X1f4_E4_LEFT_XSET flag appear in the
flags flags list
struct x1f4_operator_type record defining an infix binary
operator, the operator may set its first argument.
See Infix Binary Operator Flags.
See struct x1f4_operator_type.
It is not required that the value of its first argument is the same as the returned value. Conversely, nor is the returned copied in its first argument.
The first argument of side effects operators must be an lvalue, i.e. a variable, yet not read only one. Expressions in which the first argument of side effects operators is not an lvalue are invalid.
Note that an operator cannot overwrite its arguments in any other conditions. The operator arguments are temporary storage space and overwritting them has no effect.