A text input area with a popup, which typically presents a dropdown list of choices, but could just as easily provide choices in other ways. The user can always choose to enter their own arbitrary text as well; they are not limited to the indicated choices. See ListComboBox, ColorSwatchComboBox, or DateComboBox for typical subclasses.

The HTML5 specification calls for a datagrid element which can be used to create combo boxes, but that only supports a rather narrow definition of what a combo box can do. Even once datagrid is broadly supported, the ComboBox class still has a role to play as a base class for custom combo boxes.