In terms of syntax, what distinguishes markup languages?

Markup languages are distinct primarily due to their use of tags to format and structure content. This tag-based system allows for the clear delineation of various elements within the text, such as headings, paragraphs, links, and images. For example, in HTML, tags like

and

serve to identify and format specific types of content, enabling both the browser and developers to understand how content should be displayed and organized visually. This characteristic of using tags is what fundamentally differentiates markup languages from other programming languages, which may focus more on computation and logic rather than presentation and structure.

The other options do not accurately describe the defining syntax of markup languages. For instance, while some markup languages could include numerical data or variables, that's not a defining characteristic. Furthermore, they do not inherently incorporate specific data types as programming languages do. Lastly, while some markup languages might be interpreted by browsers, it is not a universal rule that applies across all markup languages.