XHTML Authoring Skill
Syntax Rules (MUST follow)
- Self-closing void elements:
<br/>,<hr/>,<img/>,<meta/>,<link/>,<input/> - Lowercase everything: Tags and attributes must be lowercase
- Quote all attributes: Always use double quotes
attr="value" - Close all tags: No implicit closing
- Single h1: One
<h1>per page only - Lowercase doctype: Use
<!doctype html>not<!DOCTYPE html>
Semantic Structure (MUST use)
Use semantic HTML5 elements instead of <div>:
| Element | Purpose |
|---|---|
<header> | Page or section header |
<nav> | Navigation blocks |
<main> | Primary content (one per page) |
<article> | Self-contained content |
<section> | Thematic grouping with heading |
<aside> | Tangentially related content |
<footer> | Page or section footer |
<figure> | Self-contained media with caption |
<figcaption> | Caption for figure |
<hgroup> | Heading group |
Div Alternatives (NEVER use <div>)
The <div> element is blacklisted in this project. Always use semantic alternatives:
| Instead of... | Use... |
|---|---|
<div class="header"> | <header> |
<div class="nav"> | <nav> |
<div class="footer"> | <footer> |
<div class="sidebar"> | <aside> |
<div class="content"> | <main> or <article> |
<div class="section"> | <section> with heading |
<div class="card"> | <article> or custom element like <product-card> |
<div class="wrapper"> | Style the parent element directly |
<div class="container"> | Use CSS on <body> or parent landmark |
<div class="grid"> | <ul> or <ol> with CSS grid |
Layout Wrappers
For layout constraints (centering, max-width), apply CSS directly to semantic elements:
/* Instead of <div class="header-content"> inside <header> */
header {
max-width: var(--max-width);
margin-inline: auto;
padding-inline: var(--space-md);
}
/* For edge-to-edge backgrounds with centered content */
header {
background: var(--color-primary);
/* Use padding for the content area */
padding: var(--space-md) max(var(--space-md), calc((100% - var(--max-width)) / 2));
}When No Semantic Element Exists
If you truly need a generic container (rare), use a custom element with semantic naming:
<x-layout-grid>...</x-layout-grid>
<x-card-group>...</x-card-group>Template
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1"/>
<title>Page Title</title>
</head>
<body>
<header>
<nav aria-label="Main navigation">
<ul>
<li><a href="#main">Skip to content</a></li>
</ul>
</nav>
<h1>Main Heading</h1>
</header>
<main id="main">
<article>
<h2>Article Title</h2>
<p>Content here.</p>
</article>
</main>
<footer>
<p>Footer content</p>
</footer>
</body>
</html>Void Elements (self-closing)
These elements MUST use self-closing syntax:
<area/>
<base/>
<br/>
<col/>
<embed/>
<hr/>
<img src="photo.jpg" alt="Description"/>
<input type="text" name="field"/>
<link rel="stylesheet" href="style.css"/>
<meta charset="utf-8"/>
<source src="video.mp4" type="video/mp4"/>
<track src="captions.vtt" kind="captions"/>
<wbr/>Custom Elements
- Defined elements: Check
elements.jsonfor available custom elements - Ad-hoc elements: Use
x-*prefix for one-off custom elements
See SYNTAX.md for complete syntax rules. See ELEMENTS.md for semantic element guidance. See EXAMPLES.md for code examples.
Skills to Consider Before Writing
When creating HTML, also invoke these skills based on content:
| Content Type | Invoke Skill | Why |
|---|---|---|
| Any icon or visual indicator | icons | Use <icon-wc>, never inline SVG |
| Form elements | forms | Use <form-field> custom element |
| Images | responsive-images | Use <picture> with srcset |
| Page head content | metadata | SEO, social, performance hints |
| Dialogs, popovers, toggles | progressive-enhancement | Use command/commandfor attributes |
| Interactive elements | accessibility-checker | WCAG2AA compliance |
Critical: Icons
NEVER use inline SVGs. When adding any visual indicator, icon button, or toggle with an icon:
<!-- WRONG -->
<svg viewBox="0 0 24 24">...</svg>
<!-- CORRECT - invoke icons skill first -->
<icon-wc name="menu" label="Menu"></icon-wc>See the icons skill for the full pattern.
Critical: Interactive Elements
Use declarative command/commandfor attributes for dialogs and popovers—never onclick:
<!-- WRONG - inline JavaScript -->
<button onclick="document.getElementById('modal').showModal()">
Open
</button>
<!-- CORRECT - declarative attributes -->
<button commandfor="modal" command="show-modal">
Open
</button>
<dialog id="modal">
<h2>Modal Title</h2>
<button commandfor="modal" command="close">Close</button>
</dialog>
<!-- CORRECT - popover pattern -->
<button commandfor="menu" command="toggle-popover">
Menu
</button>
<nav popover id="menu">
<!-- Navigation items -->
</nav>| Command | Target | Effect |
|---|---|---|
show-modal | <dialog> | Opens as modal |
close | <dialog> | Closes dialog |
toggle-popover | [popover] | Toggles popover |
show-popover | [popover] | Opens popover |
hide-popover | [popover] | Closes popover |
See the progressive-enhancement skill for complete patterns.
Related Skills
- icons - Lucide icon library with
<icon-wc>Web Component - forms - HTML-first form patterns with CSS-only validation
- responsive-images - Modern responsive image techniques
- metadata - HTML metadata and head content
- progressive-enhancement - Declarative dialogs/popovers with
command/commandfor - accessibility-checker - Ensure WCAG2AA accessibility compliance
- css-author - Modern CSS organization with @layer
- javascript-author - Vanilla JavaScript for Web Components