basic[SLASH]layer.yaml

provides:
  packages:
    type: array
    description: apt-packages to install

django[SLASH]layer.yaml

includes: ['layer:basic']
options:
  basic:
    packages:
      - python-dev
provides:
  source:
    type: string
    description: source of django application
  install-path:
    type: string
    description: server install path
    default: /opt/django
  something-else:
    type: object
    description: an object
    properties:
      key:
        type: <type>
        description: ...
        default: ...
        

ubucon[SLASH]layer.yaml

includes: ['layer:django']
options:
  django:
    source: "lp:ubucon"
    install-path: "/srv"
  basic:
    packages:
      - obama