Extension Fields are a standard YAML feature that helps you avoid repeating yourself in configuration files.

base_character_stats: &base_stats
  hp: 100
  mp: 50
  level: 1
  inventory_size: 10
  faction: "neutral"

characters:
  player_warrior:
    name: "Conan"
    class: "Warrior"
    <<: *base_stats
    weapon: "Sword"

  boss_orc:
    name: "Grommash"
    class: "Warchief"
    <<: *base_stats
    # You can still override things
    hp: 500
    faction: "horde"
    special_ability: "Rage"