This function will increment the value of the property by the amount passed into the function.
E.g. for a property "Total Orders" which is configured to set the value when the "place order" event occurs, and the function is passed the literal value 1, the function will increment the value of the property by 1.
The function can be passed any number value to increment by. E.g. for a property "Total Items Purchased", the function could be called with the value of "Items" to increment the value by the number of items ordered in that purchase