%YAML 1.1
---
!!map {
  ? !!str "sequence"
  : !!seq [
    !!str "one", !!str "two"
  ],
  ? !!str "mapping"
  : !!map {
    ? !!str "sky" : !!str "blue",
#    ? !!str "sea" : !!str "green",
    ? !!map { ? !!str "sea" : !!str "green" } : !!null "",
  }
}
