semantic-html

# Semantic HTML Write HTML that conveys meaning, serves all users, and respects the web platform. ## When to Use This Skill Use this skill when: - Creating new components or page sections - Reviewing markup for accessibility and semantics - Deciding between native HTML elements and ARIA attributes - Structuring documents with proper heading hierarchy - Making interactive elements accessible - Building forms with proper labelling and error handling - Creating responsive tables ## Core Principles ### Content Realism Design content is idealized. Real content is messy. Always account for: - Long sentences and long words - Images with varying aspect ratios and sizes - Multi-language support (even if not planned—users can translate via browser) - Dynamic content that changes in length and structure Build components that handle real-world content gracefully, not just what looks good in design tools. ### Landmarks-First Planning Before diving into individual components, consider the full page structure. This allows you to: - Identify key landmarks for assistive technology users - Plan heading hierarchy across the document - Make informed decisions about element choice - Avoid overusing landmarks (which diminishes their usefulness) ### Native Over ARIA Follow the first rule of ARIA: if a native HTML element provides the semantics and behaviour you need, use it instead of adding ARIA to a generic element. **Red flag:** High div count combined with high ARIA count on non-complex components signals reaching for patches rather than foundations. #### Redundant ARIA Adding ARIA to elements that already carry the correct semantics is noise—it clutters the code, can confuse assistive technology, and obscures genuine intent: ```html <!-- Redundant: <ul> already has list semantics --> <ul role="list"> ... </ul> <!-- Redundant: alt="" already suppresses the accessible name --> <img src="avatar.png" alt="" role="presentation" /> <!-- Redundant: aria-label duplicates visible text the AT will already read --> <span aria-label="Most Popular">Most Popular</span> ``` #### Don't Override Native Semantics with role ARIA `role` changes how assistive technology interprets an element. Applying a role that changes a native element's semantics introduces inconsistency—native behaviour (keyboard interaction, states, events) stays the same while the announced role changes: ```html <!-- Wrong: role="switch" changes what AT announces, but the element still behaves like a checkbox. Use the native checkbox if switch toggle semantics aren't needed, or build a proper switch widget. --> <input type="checkbox" role="switch" /> <!-- Right: native checkbox, no role override needed --> <input type="checkbox" /> ``` Only add a `role` attribute to a native element when you deliberately need different semantics and the element's behaviour genuinely matches that role. ### Separation of Visual and Semantic Hierarchy Visual styling and semantic meaning are related but not coupled. CSS classes bridge the gap: - Use the appropriate heading level based on document structure - Apply CSS classes to control visual appearance (size, weight, colour) - Create utility classes like `.u-Heading-XXL` for consistent visual treatment regardless of semantic level ## Document Structure ### Skip Navigation Links Skip links let keyboard and screen reader users bypass repeated navigation blocks and jump directly to meaningful content. They are required on any page with a navigation block or other repeated content before the main content. Place skip links as the **first focusable element** in `<body>`. They can be visually hidden and revealed on focus: ```html <body> <a href="#main-content" class="skip-link">Skip to main content</a> <!-- optional additional skip targets --> <a href="#search" class="skip-link">Skip to search</a> <header>...</header> <nav>...</nav> <main id="main-content" tabindex="-1">...</main> </body> ``` ```css .skip-link { position: absolute; transform: translateY(-100%); } .skip-link:focus { transform: translateY(0); } ``` **Why `tabindex="-1"` on `<main>`:** The `<main>` element is not natively focusable. Without `tabindex="-1"`, activating the skip link scrolls to the element but does not move keyboard focus there in all browsers. Adding `tabindex="-1"` makes it programmatically focusable (reachable via the skip link or `.focus()`) without adding it to the natural tab order. **When to add more skip links:** If the page has a prominent search bar, a sidebar, or a long secondary navigation, consider skip links to those targets too. The goal is reducing the number of Tab presses to reach primary content. **Sidebar layouts need a "skip to navigation" link:** When a sidebar navigation is placed away from the top of the DOM (e.g., after `<main>` in source order, or deep within the layout), add a skip link pointing to the `<nav>` so keyboard users can reach it without tabbing through all main content first. **The primary skip link should target `<main>`:** The first skip link should always point to `<main id="main-content">`. Additional skip links can target other meaningful landmarks or controls—a `<search>` element, a sidebar `<nav>`, or a prominent form—depending on the page's complexity. **Why this matters:** Without skip links, keyboard users must tab through every navigation item on every page load. On a nav with 12 links, that's 12 extra keystrokes — on every page. ### Landmark Elements Use landmark elements to convey page structure: | Element | Use When | Notes | | --------- | ---------------------------- | -------------------------------------------------------------------------------- | | `header` | Page or section header | Can appear multiple times in different contexts | | `footer` | Page or section footer | Contact info, copyright, related links | | `nav` | Navigation sections | Must be labelled; avoid "navigation" in the label (screen readers announce this) | | `main` | Primary content | Only one per page; must contain the primary `<h1>` | | `aside` | Tangentially related content | Content removable without changing the page's main story (sidebars, ads) | | `search` | Search functionality | Contains the search form, not the results | | `form` | User input | Only becomes a landmark when labelled via `aria-labelledby` or `aria-label` | | `article` | Self-contained content | Would make sense syndicated or standalone | | `section` | Thematic grouping | Only becomes a landmark when labelled | #### `<main>` must contain the primary `<h1>` Screen reader users often jump directly to `<main>`. If the page `<h1>` sits in a `<div>` between `<header>` and `<main>`, these users land after the title and lose essential context. The `<h1>` (and any subtitle or intro copy introducing the page) belongs inside `<main>`: ```html <!-- Wrong: h1 is outside main --> <header>...</header> <div class="page-header"><h1>FAQ</h1></div> <main> <!-- screen reader users start here, after the title --> </main> <!-- Right: h1 is the first heading inside main --> <header>...</header> <main id="main-content" tabindex="-1"> <h1>FAQ</h1> ... </main> ``` ### The Section Element A `section` without an accessible name behaves like a `div` semantically. When using `section`: - Associate it with a heading via `aria-labelledby` - This transforms it into a valid landmark region - If you cannot provide a meaningful label, question whether `section` is the right choice ### The Article Element Think beyond blog posts. Use `article` for any self-contained content that would make sense on its own: - Blog posts and news articles - Comments on a post - Product cards in a listing - Social media posts in a feed - Forum posts **Test:** Would this content make sense if extracted and placed elsewhere with no surrounding context? ### The Address Element Often misunderstood. From the HTML specification: > The address element represents the contact information for its nearest article or body element ancestor. Use for contact information about the author or owner—not for generic postal addresses. For postal addresses, use a standard `<p>` or structured markup appropriate to the context. ### `<aside>` vs `<section>` **The test for `<aside>`:** Would this content make sense if it were removed from the page entirely? Would the main content still be complete? - An advertisement, a related article link, or a biographical note about the author → `<aside>` (removing it doesn't change the main message) - A "Still need help?" CTA on an FAQ page, a summary of key findings in an article, or a prominent signup prompt → `<section>` (removing it leaves the page feeling incomplete or breaks the intended flow) When in doubt: if the content serves the primary purpose of the page, it belongs in a labelled `<section>`, not `<aside>`. ### The Aside Element and Pull Quotes `<aside>` is appropriate for pull quotes—a typographic device that highlights text from the article. However, do not use `<blockquote>` for a pull quote drawn from the page's own content. `<blockquote>` signals an external or distinct quotation. For a pull quote that restates something from the same article, use `<p>` (or styled text) inside `<aside>`: ```html <!-- Correct: pull quote from the article's own content --> <aside aria-label="Pull quote"> <p>"The biggest gains came not from new features, but from removing old ones."</p> </aside> <!-- Use blockquote for genuine external quotations --> <blockquote cite="https://example.com/source"> <p>Quote from an external source.</p> </blockquote> ``` ## Headings ### Heading Hierarchy Maintain a logical heading structure: - One `h1` per page (typically the main title) - Don't skip levels (h1 → h3) - Headings create an outline—ensure it makes sense when read in sequence ### Headings in Components For reusable components containing headings: 1. **Make heading level configurable** — Components may appear in different contexts 2. **Provide sensible defaults** — Not all content authors understand heading hierarchy 3. **Consider inheritance** — Generic components become specific ones; heading config should flow through **Example pattern:** ``` Card (generic) → heading level configurable, default h3 └─ ProductCard (specific) → inherits config, may set default based on known context └─ Used in section with h2 → heading level set to h3 ``` ### Visual Heading Without Semantic Heading Sometimes text looks like a heading but shouldn't be one semantically. Use CSS classes to apply heading-like styling without affecting document outline: ```html <p class="u-Heading-L">This looks like a heading</p> ``` ## Lists ### When to Use Lists Lists are most useful when **knowing the number of items helps the user**: - Navigation menus (how many options?) - Search results (how many matches?) - Image galleries (how many images?) - Steps in a process **Questions to ask:** - Are these items genuinely peers? - Would removing one make the others feel incomplete? - Is there an implicit "here are N things" being communicated? ### List Types | Type | Use When | Example | | ------ | ---------------------------------------- | ------------------------------------- | | `ul` | Unordered collection where count matters | Nav items, search results | | `ol` | Sequential steps or ranked items | Recipes, instructions, top-10 lists | | `dl` | Term-description pairs | Glossaries, metadata, key-value pairs | | `menu` | Toolbar commands | Action buttons, not navigation | **Ordered list attributes:** Use `reversed` for countdown-style lists (e.g., a top 10 listed from 10 to 1). Use `start` to begin numbering from a specific value. Both are native HTML—no JavaScript required. ### Definition Lists Often overlooked or confused with `details`/`summary`. Use `dl` for: - Glossary definitions - Metadata display (label: value pairs) - Any term with one or more descriptions Note: A single `dt` can have multiple `dd` elements for multiple related descriptions. ### Decorative List Separators When using CSS `::before` or `::after` to inject visual separators (e.g., breadcrumb `›`), browsers automatically exclude generated content from the accessibility tree—no extra markup is required. Do **not** try to hide it with `aria-hidden: "true"` as a CSS property; that is invalid and has no effect. If injecting separators via HTML (not CSS), use `<span aria-hidden="true">` on the HTML element. ## Interactive Elements ### Buttons vs Links **Traditional rule:** Buttons do things, links go places. **Progressive enhancement lens:** If a URL provides a meaningful fallback when JavaScript fails, a link is valid even for action-like interactions. | Interaction | Default Choice | Consider Link When | | ----------------------- | -------------- | --------------------------------------------- | | Show more content | `button` | URL params could load the content server-side | | Toggle view (grid/list) | `button` | URL could preserve view preference | | Copy to clipboard | `button` | Copied content is a shareable URL | | Tab selection | `button` | URL could load specific tab content | **Key question:** What happens when JavaScript fails? If a URL provides graceful degradation, a link may be the better choice. ### Unique Accessible Names for Repeated Buttons When the same action appears multiple times on a page (e.g., "Add to cart" on each product card, "Read more" on each article), each button needs a unique accessible name so screen reader users understand which item it acts on. Approaches (choose the simplest): ```html <!-- Option 1: aria-label with full context --> <button aria-label="Add Nike Pegasus 41 to cart">Add to cart</button> <!-- Option 2: visually hidden text --> <button> Add to cart <span class="visually-hidden">Nike Pegasus 41</span> </button> <!-- Option 3: aria-describedby pointing to the product heading --> <article> <h3 id="product-42">Nike Pegasus 41</h3> ... <button aria-describedby="product-42">Add to cart</button> </article> ``` The visible label should stay as "Add to cart" (sighted users understand context from position); the accessible name adds the product name for users who navigate by button list. ### Disabling Controls `aria-disabled="true"` communicates disabled state but does **not** prevent interaction. For buttons, `disabled` both communicates state and suppresses clicks and keyboard activation. For links, `aria-disabled="true"` alone is insufficient—it still receives focus and activates. Options: - Use a `<button disabled>` instead of a link when the action is truly unavailable - Remove the `href` attribute to prevent activation (link becomes non-interactive) - Handle `keydown`/`click` events explicitly if you must keep the element focusable ### The Popover API for Lightweight Overlays For user dropdowns, action menus, and non-modal overlays, the **Popover API** (`popover` attribute) is the preferred modern approach — not custom ARIA widget patterns. ```html <!-- Trigger: button with popovertarget --> <button popovertarget="user-menu">