You can just type clamp, and the system will bring up the intellisense which gives you a selection of expressions you can use.
A non modal menu will also pop when you get to the action of setting the angle.
If you click on the system icon all the system expressions will appear, and you can select it from there, and fill it in manually.
clamp(self.angle, 50,150) will make sure that the angle can only be within the arc of 50 to 150 degrees.
Sprite.angle, or self.angle is the only value that can vary.
Would an example help?