Monitor the validity state of form fields and provide informative messages on invalidation.
For any submittable element on a form, the following attributes can be added, the value of which being the message displayed on state invalidation:
- badInput: the user has provided input that the browser is unable to convert.
- patternMismatch: the value does not match the specified pattern.
- rangeOverflow: the value is greater than the maximum specified by the max attribute.
- rangeUnderflow: the value is less than the minimum specified by the min attribute.
- stepMismatch: the value does not fit the rules determined by the step attribute (that is, it's not evenly divisible by the step value).
- tooLong: the value exceeds the specified maxlength for HTMLInputElement or HTMLTextAreaElement objects.
- typeMismatch: the value is not in the required syntax (when type is email or url).
- valueMissing: the element has a required attribute, but no value.