%YAML 1.1
---
!!map {
  ? !!null ""
  : !!str "value",
  ? !!str "explicit key"
  : !!str "value",
  ? !!str "simple key"
  : !!str "value",
  ? !!seq [
    !!str "collection",
    !!str "simple",
    !!str "key"
  ]
  : !!str "value"
}
