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A general description is here.
RSetReg.exe has been updated to (un)set the version-specific keys in the same way as the main installer, and to have the optional argument /Personal to (un)set the per-user rather than the per-machine keys (which need administrative access).
The MSI installer defaults to an all-user (per machine) install (by setting the ALLUSERS property to 1). This can be changed at installation, and if can be built for a user-mode install (see MkRules.dist).