<?php 

# Window_BattleItem

 def include?(item)

    $game_party.usable?(item)

  end 

<?php 

# Game_Party

 def usable?(item)

    members.any? {|actor| actor.usable?(item) }

  end 

<?php 

# Game_BattlerBase

 def usable?(item)

    return skill_conditions_met?(item) if item.is_a?(RPG::Skill)

    return item_conditions_met?(item)  if item.is_a?(RPG::Item)

    return false

  end 

<?php 

def item_conditions_met?(item)

    usable_item_conditions_met?(item) && $game_party.has_item?(item)

  end 

<?php 

def usable_item_conditions_met?(item)

    movable? && occasion_ok?(item)

  end 

<?php 

def occasion_ok?(item)

    $game_party.in_battle ? item.battle_ok? : item.menu_ok?

  end