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The WCAG guidelines are built around four principles that spell out POUR: perceivable, operable, understandable and robust. [S1]

The four principles

Perceivable content provides text alternatives for non-text content such as images, videos and audio, and sufficient color contrast. [S1]

Operable content makes all functionality accessible via keyboard navigation. [S1]

Understandable content provides clear instructions and error messages for user input. [S1]

Robust content uses valid, semantic HTML as its foundation. [S1]

Semantic HTML and headings

Semantic HTML means choosing HTML elements based on their meaning and purpose, not just their appearance. [S2]

Semantic markup helps screen readers navigate and understand page structure. [S2]

For headings, never skip levels; progress logically from h1 to h2 to h3. [S1]

Screen readers can extract all the links on a page and show them as one list, so generic link text forces users back to each link context. [S1]

Contrast targets

The lesson lists a WCAG AA minimum contrast ratio of 4.5:1 for normal text and 3:1 for large text and UI components. [S1]

Claims

• id: C1 claim: "WCAG is built around four principles that spell out POUR." source: S1 evidence: "built around four fundamental principles that spell out POUR"

• id: C2 claim: "Robust content uses valid, semantic HTML as its foundation." source: S1 evidence: "Use valid, semantic HTML as your foundation"

• id: C3 claim: "Semantic HTML chooses elements by meaning and purpose, not appearance." source: S2 evidence: "Semantic HTML means choosing HTML elements based on their meaning and purpose"

• id: C4 claim: "Heading levels should never be skipped." source: S1 evidence: "Never skip levels."

• id: C5 claim: "Screen readers can list all links on a page." source: S1 evidence: "screen readers can extract all the links from a page"

Sources

• [S1] Creating Accessible Web Pages. Microsoft Web Dev for Beginners (GitHub). https://github.com/microsoft/Web-Dev-For-Beginners/blob/main/1-getting-started-lessons/3-accessibility/README.md MIT; accessed 2026-11-05.
• [S2] Terrarium Project Part 1: Introduction to HTML. Microsoft Web Dev for Beginners (GitHub). https://github.com/microsoft/Web-Dev-For-Beginners/blob/main/3-terrarium/1-intro-to-html/README.md MIT; accessed 2026-11-05.

Attribution: source authors named above; adapted summaries, not endorsed by them. MIT notices: Copyright (c) Microsoft Corporation, MIT License.

@misc{iil_note_w1w8rayg,
  author = {{Librarian}},
  title = {{Web accessibility basics: POUR, semantic HTML and headings}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-05},
  url = {https://iinventedlight.com/library/notes/web-accessibility-pour-semantic-html/},
  note = {Permanent ID iil:note:w1w8rayg. License: CC-BY-4.0.},
}

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