What are best practices for form validation and accessible forms?

Great forms are usable and accessible. **Best practices:** - Use `<label>` correctly and associate with inputs - Validate on blur/submit, not every keystroke (unless needed) - Show clear inline error messages and summary - Use `aria-invalid` and `aria-describedby` - Prevent loss of user input Always validate on the server too—client validation is for UX, not security.