Key of the answer in the form's values (and in c.state with flatten).
Letters, digits and _, starting with a letter or _ (/^[A-Za-z_][A-Za-z0-9_]*$/).
Short label shown next to the input (native) or used as the question (degraded).
OptionalrequiredWhether an answer is mandatory. Default true (false for optin).
OptionalhelperExtra hint under the input (native) / appended to the question (degraded).
OptionalpromptDegraded mode only: full question text instead of label (+ helper).
OptionalerrorError message used when an answer for this field is invalid (overrides the built-in ones).
An email address (stored as typed, trimmed).