Which of the following is a characteristic of ID selectors?

ID selectors are defined by using the '#' symbol followed by a unique identifier that represents a single element on a page. The key characteristic that distinguishes ID selectors from other types of selectors, such as class selectors, is that an ID must be unique within a page's HTML document. This means that no two elements should share the same ID. This uniqueness helps direct styles specifically and unambiguously to the appropriate element.

Specifically, the necessity for IDs to be unique ensures that any CSS styles or JavaScript functions applied to that ID will affect only one element, thereby reducing ambiguity and ensuring that the intended element is targeted without interference from other elements. This unique nature allows for clear and predictable styling and interaction within a web page.

In contrast, multiple elements can share a class selector because class selectors are not required to be unique, which allows for greater flexibility and reuse. Additionally, ID selectors have higher specificity compared to class selectors, meaning that styles defined for an ID will take precedence over styles defined for class selectors if there are conflicting styles.