X-Drive-Letter
The X-Drive-Letter field is a Boolean field that defines whether the first part of the path is viewed as a drive letter.
For example a path that starts with
/f/Path/To/File/Filename.ext
would be changed to
F:\Path\To\File\Filename.ext
This capability functions only for filenames that start the a slash, one letter (A-Z lower or upper case) and another slash.
Note that this capability is not yet implemented. The main reason for not implementing such a feature is that the destination target is expected to be respected (i.e. you cannot unpack a file outside of the --instdir path.) This kind of extraction would not work accordingly. Especially, the same package could not be installed in two different targets since files that have a specific drive defined in this way would end up in the same place for each target (although those files may be shared for certain packages, for others it may not work right at all.)
We may still look into implementing such a feature since the Microsoft Windows operating system may benefit in some ways.
The feature is being checked by the --contents command that gives you the output as expected. However, nothing else supports this feature yet.