Form and Validate

Form<T> holds a form's values, the values it started from, and what the visitor has done to it. Validate gives the rules that the browser and the server both evaluate.

Form

Put one in the page's signal struct as a field of type Form<T>.

Item	Summary
`Form::new`	A form that starts from `value`, untouched and not yet submitted.
`Form::validate`	Checks `value` against the rules of `T` on the server.

Sig<S, Form<T>>

The methods on the form's signal read and change it on the page.

Item	Summary
`value`	The values of the form.
`field`	The field `field` of the form's values, for binding a control to it.
`error`	The message to show under `field`, or `""`.
`form`	A `<form>` that, on submit, touches every field with a rule and runs `then` if every rule passes.
`touch`	A statement that marks `field` as left by the visitor.
`reset`	A statement that puts back the starting values and forgets what the visitor has done.
`is_dirty`	Whether the form's values differ from the values it started from.
`is_field_dirty`	Whether `field` differs from the value it started from.
`is_touched`	Whether the visitor has left `field`, or has submitted the form while `field` has a rule.
`is_submitted`	Whether the visitor has submitted the form since it started or was reset.
`is_valid`	Whether every rule of `T` passes for the form's values.
`reject`	A patch that shows `errors` under their fields until the next submit.

Validate and Rules

rules is generic over the page, so the same expressions are built for the browser and for Form::validate.

Item	Summary
`Validate::rules`	Adds a check to `rules` for each field of `form` that can be wrong.
`Rules::check`	Reports `message` for `field` while `ok` is false.
`FieldErrors::new`	No messages.
`FieldErrors::add`	These messages, with `message` for `field` in place of any it had.
`FieldErrors::message`	The message for `field`, if it has one.