HTML Coder Skill

Expert skill for professional HTML development with focus on semantic markup, accessibility, HTML5 features, and standards-compliant web content.

When to Use This Skill

Creating HTML documents with semantic structure
Building accessible forms with HTML5 validation
Implementing responsive markup and multimedia
Using HTML5 APIs (Canvas, SVG, Storage, Geolocation)
Troubleshooting validation or accessibility issues

Core Capabilities

Semantic HTML: Document structure, content sections, accessibility-first markup
Forms: All input types, validation attributes, fieldsets, labels
Media: Responsive images, audio/video, Canvas, SVG
HTML5 APIs: Web Storage, Geolocation, Drag & Drop, Web Workers
Accessibility: ARIA, screen reader support, WCAG compliance

Essential References

Core documentation for HTML experts:

references/add-css-style.md - Add CSS via link tag, inline, or embedded in html
references/add-javascript.md - Add JavaScript via script src="link.js" tag, inline script, or embedded in html
references/attributes.md - HTML attribute essentials
references/essentials.md - Semantic markup, validation, responsive techniques
references/global-attributes.md - Complete global attribute information
references/glossary.md - Complete HTML element and attribute reference
references/standards.md - HTML5 specifications and standards

Best Practices

Semantic HTML - Use elements that convey meaning: <article>, <nav>, <header>, <section>, <footer>, not div soup.

Accessibility First - Proper heading hierarchy, alt text, labels with inputs, keyboard navigation, ARIA when needed.

HTML5 Validation - Leverage built-in validation (required, pattern, type="email") before JavaScript.

Responsive Images - Use <picture>, srcset, and loading="lazy" for performance.

Performance - Minimize DOM depth, optimize images, defer non-critical scripts, use semantic elements.

Quick Patterns

Semantic Page Structure

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Page Title</title>
</head>
<body>
  <header><nav><!-- Navigation --></nav></header>
  <main><article><!-- Content --></article></main>
  <aside><!-- Sidebar --></aside>
  <footer><!-- Footer --></footer>
</body>
</html>

Accessible Form

<form method="post" action="/submit">
  <fieldset>
    <legend>Contact</legend>
    <label for="email">Email:</label>
    <input type="email" id="email" name="email" required
           pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$">
    <button type="submit">Send</button>
  </fieldset>
</form>

Responsive Image

<picture>
  <source media="(min-width: 1200px)" srcset="large.webp">
  <source media="(min-width: 768px)" srcset="medium.webp">
  <img src="small.jpg" alt="Description" loading="lazy">
</picture>

Troubleshooting

Validation: W3C Validator (validator.w3.org), check unclosed tags, verify nesting
Accessibility: Lighthouse audit, screen reader testing, keyboard nav, color contrast
Compatibility: Can I Use (caniuse.com), feature detection, provide fallbacks

Key Standards

WHATWG HTML Living Standard: https://html.spec.whatwg.org/
WCAG Accessibility: https://www.w3.org/WAI/WCAG21/quickref/
MDN Web Docs: https://developer.mozilla.org/en-US/docs/Web/HTML

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