how to call a model class const in a controller class?

[eluser]Unknown[/eluser]
i am new to ci, so probably a dumb question:
if i use class const in a model,

class Xmodel extends Model {
const X1 = 1;
....
}

Then how do i use it in a controller, for example? Is Xmodel::X1 available to use after loading the model?

or i should just use plain variable?

Thanks...