Validation

Summary

Built-in HTML form validation (`required`, `pattern`, `minlength`) plus the Constraint Validation API let you catch bad input before it hits the server. Validation improves user experience and data quality, but it is never a security boundary because a client can be bypassed or manipulated before a request reaches the server.

• 1Add `required` and `pattern` to a form and test invalid submissions. Test the result on both a successful path and an invalid or unexpected input.
• 2Style `:invalid` and `:valid` pseudo-classes with CSS. Validate your understanding by applying it in a small practical example.
• 3Learn why client-side validation must always be backed by server-side validation too.