188.8.131.52. Addition and subtraction operators (+, -)
These operators are both binary and unary operators. In their unary form they are used out of the precedence orders. Unary operators are always applied first, unless parentheses drive different calculation order.
If any of the operands is undef then the result is undef. If any of the operands is real the calculation is performed using real numbers and the result is real. If both operands are integer the calculation is performed using integer numbers and the result is integer.