Dawn offers support for concurrent authoring (by multiple authors or the same author working in multiple tabs).
When an edit is made by another author, a message appears at the top right of your screen letting you know that changes have been made and by whom.
Note: When you click the Save button, only the page you are editing is updated.
If you have unsaved edits on a page when an update occurs from another author, their changes will not override your edits. However, when you save, your changes will override their changes, so it's important to coordinate concurrent authoring.