Which innovative packaging design feature is credited with helping the 'Harry Potter' series achieve unprecedented sales among young readers in the early 2000s?

The book publishing industry has evolved dramatically in recent years, with innovative packaging designs helping titles stand out in both physical and digital marketplaces. Publishers now invest significantly in cover art, special editions, and unique physical features that enhance the reading experience and drive sales. Test your knowledge about a revolutionary packaging design that transformed a particular book series into a global phenomenon.

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Age-specific cover variants (different cover art for adult and child editions)
Glow-in-the-dark dust jackets that revealed hidden illustrations
Interactive AR components that animated when viewed through a smartphone
Edible bookmark inserts flavored to match themes in each book