Some extra's for fieldset components.

Better classes

The classes on taxonomy-terms has been changed to:

{%
  set classes = [
    'js-form-wrapper',
    'form-wrapper',
    'fieldset',
    element['#type'] == 'checkboxes' ? 'fieldset--checkboxes',
    element['#type'] == 'radios' ? 'fieldset--radios',
    element['#type'] == 'radios' ? 'fieldset--' ~ element['#name']|clean_class,
  ]
%}

Which gives you the following classes:

// Default Drupal classes
.js-form-wrapper {}
.form-wrapper {}

// new classes
.fieldset {}

// if the fieldset is being used by checkboxes
.fieldset--checkboxes {}

// if the fieldset is being used by radiobuttons
.fieldset--radios {}
.fieldset--name-of-radiobuttons-field {}

Note: Fieldset is by default being used by Drupal Core Checkboxes and Radio buttons. This component gives us a few classes to accomodate this.

More theme-able HTML

Instead of using the <legend> html inside <fieldset> we are using a <h3>. While being a bit less semantic, it does give us a way easier way of theming those titles. 

Theming of fieldset siblings

When using fieldsets in sequence after each other, there will be a line drawn between the different fieldsets. (screenshot 1)

Theming of nested fieldset

Fieldset's are often used inside other fieldsets by Drupal. To normalise how they look and to give us sanity theming them, the theming for nested fieldset's is resetted.

The fieldset-title of the nested fieldset will be themed the same way as normal field labels. (screenshot 2)

This is the same as the Form component but with very basic CSS added.

Better classes

The classes on a form has been changed to:

{%
  set classes = [
    'form',
    'form--' ~ element['#form_id']|clean_class
  ]
%}

Which gives you the following classes:

.form {}
.forn--user-login-form {}

Extra template suggestions

Added a more specific template suggestion. One based upon the ID of the form.

<!-- THEME DEBUG -->
<!-- THEME HOOK: 'form' -->
<!-- FILE NAME SUGGESTIONS:
   x form--user-login-form.html.twig
   * form.html.twig
-->

In above example:

• user-login-form is the ID of the form

Extra functions

Create the possibility to have form-specific preprocess functions.

So inside form--user-login-form.theme you could now have this function:

<?php

/**
 * Implements template_preprocess_hook().
 */
function compony_preprocess_form__user_login_form(&$variables, $hook) {
  // Do custom preprocessing here, 
  // only for the user-login-form. 
}

(Docs: Extending hooks yourself)