Which of the following is an example of a "constraint" in a ConstraintLayout?

In a ConstraintLayout, constraints define how views are positioned in relation to one another and to the parent layout. A constraint helps to determine the placement and alignment of a view by creating rules for its positioning.

The first option notes that a view must always be the topmost view inside a container. This represents a constraint in that it sets a rule regarding the vertical positioning of the view within the layout hierarchy. It indicates that no other views can overlap it vertically, which is a valid constraint because it ensures a specific layout behavior.

The third option specifies that a view must always be to the right of another view. This clearly expresses a horizontal relationship and sets a guideline for placement relative to another view. This too establishes a rule for positioning that directly fits within the concept of constraints in a ConstraintLayout.

Since both the first and third options depict valid placement rules within a ConstraintLayout, the combination of these two options as a correct answer accurately encapsulates what constitutes a "constraint" in this layout type. This understanding is essential in Android development, where the use of ConstraintLayout allows for more responsive and adaptable UI designs.