Are class selectors part of the Document Object Model (DOM)?

Class selectors are indeed part of the Document Object Model (DOM). The DOM represents the structure of a document, typically an HTML or XML document, as a tree of objects, where each element in the document becomes a node in the tree. Class selectors, which are used in CSS to apply styles to elements that share the same class attribute, correspond to the elements in the DOM that have that specific class.

When you define a class in your CSS, any HTML element with that class can be targeted by the class selector to apply styles. For example, if multiple HTML elements have the class "example," they can all be styled collectively by the class selector in your CSS. As a result, class selectors are integral to the way styles are applied to elements in the DOM, connecting the visual representation of the page to its underlying structure.

The other choices indicate nuances that are less accurate. There isn’t a distinction in DOM integration based on whether they are defined in CSS3, used multiple times, or part of the overall object of a web document. Class selectors simply reflect the capability to target elements in the DOM based on shared attributes. Thus, the understanding that class selectors are part of the DOM is fundamental to web development and styling practices.