PowerType question

[zork]

I checked. This was the powertype list as of patch 5.0.5

    0 - Mana (SPELL_POWER_MANA)
    1 - Rage (SPELL_POWER_RAGE)
    2 - Focus (SPELL_POWER_FOCUS)
    3 - Energy (SPELL_POWER_ENERGY)
    4 - Happiness (SPELL_POWER_HAPPINESS)
    5 - Runes (SPELL_POWER_RUNES)
    6 - Runic Power (SPELL_POWER_RUNIC_POWER)
    7 - Soul Shards (SPELL_POWER_SOUL_SHARDS)
    8 - Eclipse (SPELL_POWER_ECLIPSE)
    9 - Holy Power (SPELL_POWER_HOLY_POWER)
    10 - Alternate Power (SPELL_POWER_ALTERNATE_POWER)
    11 - Dark Force (SPELL_POWER_DARK_FORCE)
    12 - Light Force (SPELL_POWER_LIGHT_FORCE)
    13 - Shadow Orbs (SPELL_POWER_SHADOW_ORBS)
    14 - Burning Embers (SPELL_POWER_BURNING_EMBERS)
    15 - Demonic Fury (SPELL_POWER_DEMONIC_FURY)

12 got replaced by SPELL_POWER_CHI in patch 5.1

But what the heck is DARK_FORCE? When does this get used?