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HTML Validation Guidelines
Document Structure
- Include DOCTYPE declaration
- Use html, head, and body elements
- Include title element in head
- Proper element nesting
- Close all non-void elements
HTML5 Standards
- Use semantic HTML5 elements
- Declare character encoding
- Include viewport meta tag
- Avoid deprecated elements
- Use valid attribute values
Accessibility
- Provide alt text for images
- Use proper heading hierarchy
- Label form elements
- Ensure keyboard navigation
- Use ARIA attributes when needed
HTML Validation Reference
Common Errors
- Unclosed or mismatched tags
- Missing required attributes
- Invalid attribute values
- Improper element nesting
- Missing DOCTYPE or meta charset
Validation Tools
- W3C Markup Validator
- HTML5 Validator
- Browser Developer Tools
- Accessibility checkers
- Lighthouse audits
Best Practices
- Validate early and often
- Use semantic markup
- Follow accessibility guidelines
- Test across browsers
- Keep markup clean and readable