mixin - includes another set of fields.
_include1: type: mixin source: <uuid|handle>
When using a mixin, consider prefixing the field name with an underscore (_) to make them easy to spot.
To include a mixin, you may reference the
source as the blueprint handle.
_location_fields: type: mixin source: Fields\Location
For a more robust reference, you may also specify the UUID.
_blog_fields: type: mixin source: 6d6a5efa-3ce7-4b9d-bddc-ac48867552cb
See the Blueprints article for more information on defining mixins.