What are Constrain Attributes For?

hardsoft

So I am reading the Gamesalad manual where you recreate the basic shoot em' up and they say that I need to create a constrain attribute to constantly update the x and y position of the player ship. What I don't get is , what is the point of the constrain attribute? Because I feel like the game can do perfectly fine without it. Can someone explain to me what it is for? Because the definition in the cookbook and the game creator itself is not clear at all.

SolarPepperStudios

Constrain attribute constantly updates the variables whereas change attribute only updates (changes) it once. So it you were to drag a ship around with your mouse you would do:
When mouse button is down, constrain ship.x to mouse.position.x (do the same for Y)
and constrain self.position.x to ship.x (same for Y)

SolarPepperStudios

Here is an example:
https://dl.dropbox.com/s/jltzrcvou8sfsgu/Drag.zip?token_hash=AAFNvBtvAfTrnkeIlU9E_yB2vGVpWDDPT0bOFKQs6QX5Wg&dl=1