Declaring a Record Type using Case.

[jsosnowski]

I just ran across some code that declares a complex packed record:

aSInt = Integer;

entity = packed Record
   Enttype : byte;   
   field2 : double;
   ... //continues with other standard fields and then uses this case 
      CASE aSInt OF
       entlin: (linpt1,
            linpt2: point);
         entln3: (ln3pt1,
            ln3pt2: point);
         entmrk: (mrkpnt,
            mrkvec: point;
            mrktyp,
            mrksiz: aSInt);  
            ... //other case types
      End;
end;

The entlin, entln3, entmrk are constants used to identify specific types.
This code confuses me. The case statement is using an aSint, which is an integer, but does not assign it to a variable such as with this:

Case Etype of 
       entlin: (linpt1,
            linpt2: point);
       ...//etc.

where Etype is a variable that conveys the type constant to apply.

How is this code used without an identification of what the aSint? How is the Asint value passed on when the record is used since it varies in size and the type of each instance must known to determine its size and allocate memory and read the data?