Slugline does not use the new document model Apple introduced in OS X Lion. Many writers prefer to manually save their documents, and to have access to useful menu items such as Save As and Revert to Saved.
This means that Slugline does not automatically save changes to your document as you work. However, we do auto-save to a backup file in your Library folder. If Slugline is interrupted, we’ll use that version to attempt to recover your work. If you try to exit Slugline without saving, we warn you, and ask you what you want to do.
To save versions of a screenplay, we highly recommend using File → Save As to create separate files for each version. We’re old fashioned that way.