These notes connect to the contact form I built for HW4.

Built-in HTML validation

• required, minlength, maxlength, and pattern attributes help control input.
• Semantic types like <input type="email"> add extra validation for free.
• Browser handles basic error messages and focus.

Custom validation

• JavaScript can hook into the Constraint Validation API:
  • checkValidity() to test the field or form.
  • setCustomValidity() to provide a clearer error message.
• We can combine this with our own error <output> element to show messages in a11y-friendly ways.