After Effects Nomenclature
The checkbox control, or checkbox, is an expression control, which can be animated, and is used in After Effects when a Boolean value (on/off, true/false, or two choice variable), is needed to control a property via an expression. The checkbox returns one of two values: 0 if it is not checked; 1 if it is checked.
The checkbox control is accessed through the menu Effect > Expression Controls > Checkbox Control.
The checkbox can be very useful in puppet rigs. For example, if you wanted your After Effects puppet to be able to wink with either eye, you could use an expression connected to a slider with a label of Right Eye Bink to close and open the right eyelids. Then you could create another expression to make the left eye wink, connecting it to a different slider labeled Left Eye Bink. This would allow you to easily have your character wink. Unfortunately, to make it blink with both eyes, which would be the dominate action for the eyelids, you would have to move both sliders, which means moving two sliders every time you wanted your character to blink.
However, you could add a checkbox control along with an if/else statement to the Left Eye Wink expression1. That statement could tell the left eyelids to use the value of the Left Eye Bink slider when the checkbox is not checked, but use the Right Bink Slider values when the checkbox is checked. That way you could check the checkbox and only have to move the Right Eye Bink slider to create a blink. When you’re ready for your character to wink, uncheck the box and they can bink with either eye.
1Of course, selecting the left eye expression instead of the right eye expression in this example is arbitrary, just as is what condition you want to use to trigger the wink vs. the blink.