The JS Active Field module is used to apply a modifier class,
.js-active-field elements whose child
textarea element has focus and/or a nonempty value. The
is-active class, in turn, is used to achieve styling that indicates to the user which form fields have either been filled out already, or are currently being filled out.
While the application of style rules via the
is-active class is entirely open, one particularly common pattern is implemented by
form__item--dynamic-label, shown below.