Which innovative brand storytelling technique, first widely used for J.K. Rowling's Harry Potter series, revolutionized how literary works connect with audiences?

In the world of literature, brand storytelling has evolved dramatically over the decades. Publishers and authors have found innovative ways to connect with readers beyond just the pages of a book. One particular revolutionary approach changed how literary works were marketed forever, creating deeper connections between readers and the worlds authors created. Test your knowledge about this significant milestone in literary brand storytelling!

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Immersive themed retail environments (like Platform 9¾ installations in bookstores)
Author video blogs explaining character backstories
Limited edition covers with hidden messages visible only under UV light
Reader-submitted fan fiction published as official companion works