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• Categories are groups of pre-defined content that identify the primary topics of your site. In general, content only belongs to one category. For example, in the Magnolia Travel Demo, tours are organized into categories such as Europe, Asia and Africa.
• Tags are free-form and can be defined by authors on the fly. Multiple tags can be applied to many content items. For example, in the Travel demo, a tour can be tagged adventure regardless of whether it takes place in Europe, Asia or Africa. 

Ease-of-use

Once tagging is enabled for a content app, authors can create and apply tags by selecting a item and clicking the Add or Modify tags action (depending on the app currently in use) to open the tagging dialog. When you start typing in the Tags field, Magnolia suggests tags that already exist. 

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