Headings in HTML5 may be presented to users differently based on the document structure, particularly within <section> and <article> elements. Headings within these elements are isolated from the surrounding document, but when presented to end users the heading level may be shifted up or down based on surrounding content and preceding headings. For example, an <h1> heading in an <article> may be presented as a second-level heading if there is a preceding <h1> in the document. To ensure the HTML5 outline is accurate and logical, use the HTML5 Outliner to view how headings will be presented to end users.
