There are multiple sets of holes along the external sides of the handle housing. The toggle buttons of the handle (sometimes referred to as 'spring clips') lock into these holes, raising and lowering the height of the retractable handle.

Check the function of this mechanism by pressing the handle's release button and watching the toggle buttons:

When the luggage handle is fully functional, the handle release button causes these toggle buttons to fully retract into the holes.

When the luggage handle mechanism is sticky or fully stuck, the handle release button does not cause the toggle buttons to retract properly.