What does the class attribute do in HTML elements?

The class attribute in HTML elements is used to apply styles to a specific group of elements. By assigning the same class name to multiple elements, you can target them collectively in your CSS. This allows for consistent styling across those elements without needing to apply individual styles to each one.

For instance, if you have several <div> elements that you want to have the same background color, you can assign them all the same class name and then create a single CSS rule for that class. This approach enhances maintainability and reduces the amount of code needed, as changes to styling can be made in just one location in the CSS file, affecting all elements that share that class.

Other answer choices refer to different functionalities: referencing external stylesheets is done using the link element, unique identifiers are handled by the id attribute, and the visibility of elements typically is controlled through CSS properties like display or visibility rather than the class attribute itself.