What does Rule 21 cover regarding lights and shapes?

Rule 21 of the COLREGs, titled "Definitions," does cover the exhibition of proper lights for various types of vessels. This rule provides essential definitions related to navigation lights and shapes, which are crucial for safe navigation, particularly at night or during periods of restricted visibility.

By establishing how different classes of vessels are required to display their lights, Rule 21 helps to ensure that mariners can identify the type and status of approaching vessels, which is critical for preventing collisions at sea. Understanding these requirements helps navigators recognize whether a vessel is at anchor, underway, or engaged in fishing, among other activities, thus promoting safe maritime practices.

The other options do not accurately reflect the focus of Rule 21. The requirement to exhibit lights is a key safety aspect that directly impacts a vessel's ability to navigate safely in various conditions.