Heading outline viewer

Paste markup on the left. The outline its headings make appears on the right, with skipped levels flagged.

Markup

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    Outline

    Turn on JavaScript to compute the outline. Without it, read the sample on the left and find the three skipped levels by eye: the Menu heading, the Parking heading, and the empty heading after Gear.

      Levels come from the element names alone: no browser computes them from section or article. A skipped level breaks a rule of the HTML standard, and its flag uses the Nu HTML Checker's wording; the warnings are advice.