• Apple Human Interface Guidelines: Windows
  An item that provides click-through is one that a user can activate on an inactive window with one click, instead of clicking first to make the window active and then clicking the item. Click-through provides greater efficiency in performing such tasks as closing or resizing inactive windows, and copying or moving files. In many cases, however, click-through could confuse a user who clicks an item unintentionally.
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• Daring Fireball: The Problems With Click-Through
  in Public bookmarks with click-through daringfireball mac osx by 2 users

click-through from all users