A heading is text that introduces, labels, and structures a section of content. Headings create the hierarchical skeleton of a document: they tell the reader what each section is about and how sections relate to one another.
Headings are set with greater visual weight than body text — larger size, bolder weight, or both — so that a reader scanning the page can locate them without reading the surrounding prose. This visual distinction is functional, not decorative: it lets the reader navigate the document’s argument from its structure alone.
In HTML, headings form a six-level hierarchy from <h1> through <h6>. The <h1> element represents the page’s primary topic; subsequent levels represent increasingly specific subsections. This hierarchy carries semantic meaning: assistive technologies like screen readers use heading levels to build a navigable outline of the page, and search engines use them to understand the document’s structure. Skipping levels (placing an <h4> directly under an <h2>, for example) breaks this outline and makes the document harder to navigate for users who rely on it.
In Markdown, headings are marked with # characters: one # for a top-level heading, two for a second-level heading, and so on. Quartz and other static site generators convert these to the corresponding HTML heading elements.
Effective headings are specific. “Results” tells the reader less than “Failure rates under cyclic loading.” A reader should be able to reconstruct the document’s argument from its headings without reading the body text between them.