HTML uses ____ to annotate documents, marking up content to identify specific HTML elements.

In HTML, tags are fundamental for annotating documents. They serve as the building blocks that define the structure and meaning of the content within an HTML document. Each tag typically comes in pairs: an opening tag and a closing tag. For instance, the <p> tag indicates the start of a paragraph, while </p> denotes its end, clearly marking where the paragraph content begins and ends.

Using tags allows browsers to interpret the different elements of a webpage correctly, such as headings, paragraphs, links, images, and lists, ensuring that the content is presented appropriately to users. This systematic markup is crucial for both the rendering of the page and for search engines that crawl web pages for content indexing.

The other options, while related to HTML and web development, do not specifically refer to the mechanism HTML employs for content annotation. Syntax encompasses the rules and structure of how tags should be used but does not itself annotate content. Semantic refers to meaning and context within web content, which is enhanced by using the correct HTML tags, but does not define the marking up process itself. HTTP is a protocol for transferring data over the web and not directly involved in the markup of HTML documents.