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The page might not use rules like that though? And the browser could optimize the case where it doesn't.

• c-smile 9y ago
  That just one example. One element removal means invalidation of container's layout. That means you will need to relayout container. That is a scan of children again. And so on.
  • bzbarsky 9y ago
    An element removal may also mean absolutely nothing if the container is display:none, say...