Thank you! I'm glad that you enjoy it so much. I also just love the book and made this wiki hoping that others who also loved the book could become part of a fanbase for Wonder. I hope that you'll continue to contribute here :)
You can contribute in whatever way you want :) It would be extra helpful though to add the basic events that happen to a given character under a history section on that character's page. Though the history there can be long, you don't have to write a whole one as it can be quite tedious, whatever you can add would be helpful ;) See Miranda as an example of a history section. It's also helpful to create the pages for the characters that do not yet have pages and add basic information to them. Whatever you do to contribute, whether it's commenting on pages, adding to pages, or writing blog posts, would be helpful. I'm so glad that you love Wonder!
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