postoffice-1.0.x-dev/extensions/postoffice_file/config/schema/postoffice_file.schema.yml

field.formatter.third_party.postoffice_file:
  type: mapping
  label: 'Schema for postoffice_file module additions to entity_view_display entity'
  mapping:
    adjustment:
      type: string
      label: 'HTML email adjustment'