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A useful way to learn this is to start with the browser's observable behavior, not the tag list. In this lesson, the focus is broken nesting, missing headers, layout tables, and malformed spans. That matters because HTML is interpreted by a parser and then exposed to browser features such as navigation, accessibility tooling, form controls, media handling, and script APIs. A correct-looking screenshot can still hide a poor document model.
<table><tr><td><div>...</div></td></tr></table>
The browser's defaults are part of the behavior you are learning. Prefer native semantics first, then test the exact combination of attributes and content you plan to ship.
Warning: invalid or overly permissive markup may still render. Rendering is not proof that the document model is correct.
Start with the smallest meaningful example. The working snippet demonstrates the core syntax, but the important part is what each piece contributes: the element supplies semantics or behavior, attributes refine that meaning, and surrounding structure gives the browser context. Don't add markup just because a framework or copied example happens to include it.
<table><caption>Support queue</caption><thead><tr><th scope="col">Queue</th><th scope="col">Open</th></tr></thead><tbody><tr><th scope="row">Billing</th><td>14</td></tr></tbody></table>
The browser's defaults are part of the behavior you are learning. Prefer native semantics first, then test the exact combination of attributes and content you plan to ship.
<tr><th rowspan="2">Revenue</th><th colspan="2">Q3</th></tr><tr><td>July</td><td>August</td></tr>
In a team codebase, the expensive bugs usually come from assumptions. Someone assumes an anchor is just a button with a different visual style, that a placeholder is a label, that an iframe is only a rectangle, or that a client-side constraint is security. The safe engineering move is to name the browser behavior you actually depend on and encode it directly in HTML.
Source-reading note: the exact semantics here come from the HTML element/attribute you chose, not its CSS appearance.
Field tip: for common table structure problems, test both the ordinary path and the first case that makes your assumptions false.
Finish the lesson once you have worked through the material. This awards ★ 20 XP.