x,y,z          is the position of the connection
ox, oy, oz  is the orientation of the connection
D               is the identifier for a deleting connection command

New metacommand added inside models definition
I have added the following metacommand to allow group and belt functionality

0 GROUPLIST   Starting of group list
   0 GR Name #  All groups used in the model are listed here:
                                  GR is constant
                                  Name is the group name
                                  #  the last is a progressive group identifier
0 ENDGROUP    End of the group list

The above lines must appear before any group is used in your model

0 GROUP  #    means that the following line identify a part that belongs to  GROUP #

0 BELT # PartFile1.DAT x1 y1 z1 PartFile1.DAT x2 y2 z2
Belt             is a constant
#                is the belt progressive identification number
Partfile1.dat    is the filename of the 1st part involved in the belt
x1, y1, z1              is its position
Partfile2.dat    is the filename of the 1st part involved in the belt
x2, y2, z2       is its position

the above lines must appear in the model definition after Partfile1.dat and Partfile2.dat has been already added in the expected position, otherwise the belt will not be generated.
Patch technical issues

Command added in external files in C:\lDraw\Conns file folder

this is what I had to add to patch ldraw brick library:
C Type x y z ox oy oz            identify a new connection
G nTooth x y z ox oy oz    identify a nTooth gear connection
D Type x y z               identify a connection that need to be deleted

and G     are the identifiers for new connection command
Type         is a number that identify the type of connection and currently can be one of the following:
NotConnection = 0
Stud = 1        
'Stud* part
ToStud = 2       'Is normally in the back of the stud and is where a Stud connection can be stored
PegHole = 3      'PegHole Part
HingeM = 4       'Hinge Male
HingeF = 5       'Hinge Female
MidStud = 6      'Centre of stud2 typical part, store BackStud connections
Belt = 7         'Belt connection (added at runtime only)
Connect = 8      'Connect* Part/subpart
Friction = 10    'Crowned connections
Axle = 11        'Axle part connection
AxleHole = 12    'AxleHole part connections
MidStudUp = 13   'Connection among 4 studs up, can connect BackStud2 connections
Gearc = 14       'Gear Connection (added at runtime only when needed)
Rack = 15        'Rack connection (still not implemented)
ToStudNoHide = 16
'Like ToStud, but show connected studs
BackStud2 = 98   'BackStud Big (Stud4 part)
BackStud = 99    'BackStud Small (Stud3 part)