<input type="email" required />
<input type="text" pattern="[A-Za-z]{3,}" title="At least 3 letters" />
<input type="number" min="1" max="100" />

• required — blocks submission if the field is empty
• pattern — validates against a regular expression
• min/max/step — bound numeric and date inputs
• element.checkValidity() and :invalid CSS pseudo-class hook into the same system from JS/CSS