BCMAP - Base Class Map; Defines inheritance.
CMAP - Class Map; List all the classes in the msstyles.
RMAP - Root Map; Global properties.
VARIANT - Defines all the properties for the that variant / substyle.
VMAP - Variant Map; lists all available variants.
By variant I assume you mean the particular theme msstyles as a variant of aero.msstyles?
But then what does "all available variants" mean?