Accepting that (1) I want to use a sequence diagram and not a class, communication or any other diagram and (2) I am not using official UML specification and am prepared to bend the rules, the question is: Is it possible to demonstrate an object being passed as an argument to a function call on another object? For example, in the snippet below, object1's function "add" takes the argument "object2" (adding their respective properties), but the diagram conceals the fact. Would the aforementioned be acceptable? If so, what is the best way to do it?

Thanks in advance.

var object1 = new O("object1");
var object2 = new O("object2");
object1.add(object2);
alert(object1.name);  // object1 + object2

function O(param) {
    this.name = param;
    this.add = function(param) {
        this.name = this.name + " + " + param.name;
    };
}