.Briefcase folders are used by Data Abstract to serialize client-side data and deltas to the Folder in the client file system. In comparison to .daBriefcase Files, it holds the data for each table serialized in a separate binary file. Thus, data for each table from the briefcase can be read and loaded to the client application independently from others.
The content of the .Briefcase folder has a binary format and corresponds to the Bin2DataStreamer format. It can be opened by the Server Explorer application in the Mac OS X or the DABriefcaseExplorer tool in the Windows OS.
Briefcase custom properties are stored in the Properties.plist file in XML format.
You don't need to manually change the properties or data files. They are managed automatically by the appropriate classes.
In the Mac OS X folder, the briefcase looks like a usual file. In order to see its content, you need to perform a right click on the file and select the Show Package Contents menu item.