code: function (prop, setter) {
                    // jQuery 1.8 style
                    if ($.Tween) {
                        $.Tween.propHooks[prop] = {
                            set: setter
                        };
                        // pre 1.8
                    } else {
                        $.fx.step[prop] = setter;
                    }
                }
docs: Add an animation setter for a specific property