ckeditor5-1.0.x-dev/tests/modules/ckeditor5_test/ckeditor5_test.ckeditor5.yml

ckeditor5_test.layercake:
  library: ckeditor5_test/layercake
  plugins:
    - layerCake.SimpleBox
    - layerCake.TwoCol
  toolbar_items:
    simpleBox:
      label: Simple Box
    twoCol:
      label: Two Col layout
  elements:
    - <h1 class>
    - <div class>
    - <section class>