File 4 is $AttrDef, which contains the attribute names for all 
attributes used on the volume. Currently, only the well-known attributes 
should appear. Each definition has A0 bytes. At the beginning, the 
attribute name (Unicode) appears. It is not clear whether it is null 
terminated, or has a fixed size and is filled up with zeros. At offset 
80 is the numerical value for the attribute.  The purpose of any other 
data is not known. P. 32 gives some hints what else should be there. 