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There are some slight differences between journal entries in the app versus journal entries on LDS.org. On LDS.org, you can add tags to your journal entries. A journal entry that has a tag will also appear in the Tags section on LDS.org.
However, the Gospel Library app does not yet allow tags with journal entries, so you cannot add a tag to a journal entry. Additionally, journal entries that you tagged on LDS.org do not appear in the Tags section of the app.
In the Gospel Library iOS app, journal entries are called "notes." You can create notes only inside Documents. Any Document notes you create on an iOS device will sync as journal entries on LDS.org or as journal entries on an Android device.