Crown and tiara are currently tagged quite inconsistently. For example, some posts with a tiara are also tagged with crown, while others aren't; meanwhile, Princess Celestia's headwear is alternately tagged with only crown or tiara.
What are your thoughts on classifying crowns and tiaras? Wikipedia focuses on the context (e.g., crowns=royal symbol and tiaras=female decorative headpieces), while other sources assert that proper tiaras are semicircular unlike circular crowns.
There's also the possibility of aliasing/implicating these, if need be.
Updated by user 59725