What is in the .MD2 and .MPS 'subfiles' (inside Garmin .IMG files)?

[GPSFranz]

Here is another one of my stupid questions:

As far as I understand it, Garmin .IMG files usually contain a certain number of map tiles (.NT 'subfiles' in the newer Garmin products).
Additionally, they usually contain an .IDX 'subfile' (probably the index needed to find 'information'), a .TYP 'subfile' (to determine how the 'information' is displayed), and then the .MD2 and .MPS 'subfiles'. The .MD2 'subfiles' are from less than 100 kB to several 100 kB in size; the .MPS 'subfiles' are usually less than 50 kB.

What is in the .MD2 and .MPS 'subfiles', and how and when is this information used?
(I assume it is used for something; otherwise they would not put it in the .IMG files.)

Any ideas?

[Giomen]

MD2 is secret weapons of Garmin still now

MPS section like TDB file for Mapsoure contain a description of subfiles with maps in mapset. You can see it with the naked eye. It is name of maps and mapset, unlock code - in separate maps file there are no this info.

In Gmaptool log this is a next data (marked with red color):

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