AutoCAD has a number of commands that begin with the + character. These are usually commands that open multi-tabbed dialog boxes. By prefixing the command name with the +, AutoCAD then prompts you for the tab number, which begins with 0 for the first tab. These are primarily meant for macros and LISP routines.
Tab index <0>: (Enter an integer.)
AutoCAD 2012's new command interface lists all commands starting with the same letter. Normally, I find this a pain, since it will tend to list a closing command before an opening one. For instance, it lists MatBrowswerClose before MataBrowserOpen, since it works in alphabetical order. But how often do you need to know the name of the command for closing a palette? (Just click the X.)
Anyhow, this new command interface lists for us all command names that start with +:
Of the commands on this list, three do not display tabbed dialog boxes. They react differently:
Input save format [dwG/dwT/dwS/dwF/Other]:
+SaveAs lets you specify the file format; the Other option lets you specify the version number, ranging from 0 = AutoCAD 2010/1/2 DWG, down to 11 = AutoCAD R12 DXF.
Enter <menugroup name>,<element id> of the tab to make active (e.g. ACAD_Tabhome):
The +Ribbon command opens a specific tab in the ribbon.
Specify filter [All/All Used Layers/Unreconciled New Layers/Viewport Overrides] <All>:
The +Layer command lets you specify layer filters.