mt.exe -replacements: xml file structure for registration free COM component is not documented

Question

I am using mt.exe to generate a manifest for a registry free C++ COM component. The .rgs file passed on the command line has some replaceable strings whose value must be stored in a .xml file passed to the -replacements argument. The thing is, there is no documentation on the expected syntax for that xml file. I reported the issue to Microsoft but the ticket was closed without providing any solution. Does any one know how the replacement xml file should be structured?