Validation and errors

Form keeps all validation sources in one ordered issue model without pretending they are the same thing.

Choose the source that owns the rule

Source	Use it for
Native browser constraints	required, input type, length, and other HTML constraints
Field or application validation	Product rules that can be checked locally
Standard Schema	Authoritative input validation and output transformation
Server issues	Rejections known only after a save request

A submission failure such as a network outage is not an invalid field. Form stores it in submission state. Return field-related server issues only when the server rejected specific values.

Issue identity and focus

An issue may target one primary field and additional related fields. It appears once in the summary while every related field becomes invalid. After a failed submission, the host focuses the earliest rendered invalid field rather than depending on validator return order.

Changing a field clears server issues related to that value; unrelated input does not. validateOn and revalidateOn decide when interactive checks run, while submission always performs the complete validation pass.

For template code and message composition, see Vue validation and errors. For an existing HTML form, configure validation through DOM forms and the DOM API.