Which language is primarily used for webpage markup?

HTML5 is primarily used for webpage markup as it serves as the standard markup language for creating web pages and applications. It provides the structure and layout for content on the web, allowing developers to define elements such as headings, paragraphs, links, images, and other interactive features.

In addition to basic structure, HTML5 introduces various new elements and attributes that enhance the capabilities for multimedia and graphical content, such as audio and video support, which were less effective in previous versions. It is essential for web development because it facilitates the organization of content in a way that browsers can interpret and render effectively to users.

While other languages have specific purposes, they do not primarily fulfill the role of marking up web content. For instance, XML is more about data transport and storage rather than directly rendering web pages, CSS is primarily used for styling and visual presentation rather than markup, and JavaScript is focused on interactivity and behavior on web pages. Therefore, among the options provided, HTML5 is the clear choice as the primary language for webpage markup.