any number of instances of any element. An ID may only be applied to a single element.

Pseudo-classes

Pseudo-classes are used in CSS selectors to permit formatting based on information that is not contained in the document tree.

One example of a widely used pseudo-class is , which identifies content only when the user "points to" the visible element, usually by holding the mouse cursor over it. It is appended to a selector as in or .

A pseudo-class classifies document elements, such as or , whereas a pseudo-element

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