Reusable fields

Define the fields once in site/blueprints/custom-fields/:

# site/blueprints/custom-fields/seo.yml
type: group
fields:
  seoTitle:
    label: SEO title
    type: text
    maxlength: 60
  seoDescription:
    label: SEO description
    type: textarea

Use them in any blueprint, the group is replaced by its fields:

# site/blueprints/pages/article.yml
fields:
  title:
    type: text
  seo: custom-fields/seo

tabs:
  content:
    fields: [title]
  seo:
    label: SEO
    fields: [seo]

Single fields can be extended and adjusted, too:

# site/blueprints/custom-fields/date.yml
type: date
display: DD.MM.YYYY

fields:
  publishedAt:
    extends: custom-fields/date
    label: Published at

Whole tabs work the same way:

# site/blueprints/tabs/seo.yml
label: SEO
fields:
  seoTitle: text

tabs:
  seo: tabs/seo

Output in a partial:

<?php // site/templates/partials/head.php ?>
<title><?= $page->seoTitle()->or($page->title()) ?></title>
<meta name="description" content="<?= $page->seoDescription()->stripTags() ?>">