:optional CSS pseudo-class

The `:optional` pseudo-class matches form inputs (`<input>`, `<textarea>`, `<select>`) which are not `:required`.

input event

The `input` event is fired when the user changes the value of an `<input>` element, `<select>` element, or `<textarea>` element. By contrast, the "change" event usually only fires after the form control has lost focus.

readonly attribute of input and textarea elements

Makes the form control non-editable. Unlike the `disabled` attribute, `readonly` form controls are still included in form submissions and the user can still select (but not edit) their value text.

htmltextareaelement api: form

html element: textarea: form