Sections revealed by the triangle button can be from the current book or from another Bookvoid book. Sections from other books are not necessarily available offline. Due to size limits on local storage in browsers, the text from books you have not opened recently while online may not be available offline.
If you edited notes, starred sections or highlighted words while offline, press the sync button ( ) to save your changes to the server. A sync is automatically initiated after opening or reloading a page while online. It is possible to be signed-in locally and still be able to edit notes and highlights after the server sign in has expired. If you haven't interacted with Bookvoid while being online for a long period of time, you may need to login again for the sync to complete successfully. A "Go Online" link will be available for that purpose. The "Sign out" link signs you out of both the online and offline account. You will need a connection to the internet to sign-in again. You can read books while offline, but you can't edit notes, star sections or highlight words.