What does XHTML use to format a page's appearance in the Web browser?

The correct answer is that XHTML uses Cascading Style Sheets (CSS) to format a page's appearance in the web browser. While XHTML is fundamentally a stricter and cleaner version of HTML, the actual styling and presentation of the content within an XHTML document is generally handled by CSS.

CSS allows web developers to define styles such as colors, layouts, fonts, and spacing separately from the content, which is organized using XHTML. This separation of content and presentation is a core principle of modern web design, promoting both flexibility and maintainability. By controlling the visual style through CSS, developers can easily make site-wide changes without altering the XHTML structure.

While HTML is related and serves as a foundation for XHTML, it's CSS that directly influences how the content is displayed in a browser. JavaScript is primarily for behavior and interactivity, while XML is employed for data representation and does not control presentation in a web context. Thus, understanding the role of CSS as the correct method for formatting and styling XHTML content is crucial for web design.