When a user is in the page editor, it will automatically give the concept of a read only mode to other users with edit access. This will help to prevent save conflicts by having two or more people working on the same poster.

When one user is in the editor, all other users who have edit access will see a message in the template screen. This message will advise of the user's name who is currently editing.

You have the option to navigate in the editor and preview the poster. You will be able to select the different preview options as well and see the sections and subsections, but the edit options and icons will be hidden.

The message includes an Edit Anyways option. If you select this you will be able to start editing the poster, however for the other user currently editing, any edits that have not been saved or published will be lost. When this user goes to save or publish they will receive a message stating their editing permission has been taken away with the new users name and any unsaved data is now lost.