HTML

1. Getting started with HTML

   Elements, tags, attributes, document structure and the DOCTYPE.

2. HTML elements reference

   The full catalog of elements by purpose.

3. HTML attributes reference

   Global and element-specific attributes.

4. Global attributes

   id, class, data-*, hidden, tabindex, lang, contenteditable and inert.

5. Content categories

   Flow, phrasing, interactive and metadata content models.

6. Document and sectioning elements

   Headings, header, nav, main, section, article, aside and footer.

7. Text content and links

   Paragraphs, lists, emphasis, anchors, rel attributes and URL fragments.

8. Images and responsive images

   img, picture, srcset and sizes, alt text and lazy loading.

9. Audio and video

   video and audio elements, source, track and media controls.

10. Tables

    Table structure, caption, thead/tbody, scope and accessible tables.

11. Forms and inputs

    form, input types, label, select, textarea, fieldset and submission.

12. Constraint validation

    required, pattern, min/max, validity API and custom validity.

13. Document metadata

    head, meta, viewport, charset, link and base.

14. Scripts and resource loading

    script async/defer, modules, preload and resource hints.

15. Embedded content

    iframe, sandboxing, object, embed and canvas.

16. Interactive elements

    dialog, details/summary and popover.

17. Templates and web components

    template, slot and shadow DOM basics.

18. HTML accessibility

    Semantic HTML for assistive technology, labels, landmarks and ARIA.

19. Date formats and microdata

    Valid date and time strings, time element and structured data.

20. Quirks mode and standards mode

    Doctype-driven rendering modes.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.