I'm not exactly sure what version it is... I just had a look see and because it's built-in there is no docs on it. Do you have "use built in player" checked in RRconfig?
Your right about the synopsis stuff, there are few skins that actually use it. I believe it was a feature adopted from the late great MediaCar (if you take a look at the skin it should be in there)
Here is the docs from the skincommand.txt:
/, (R) Album TEXT art*
/, x y w h r g b pt font
/, --- --- --- --- --- --- --- -- ----
The above tag defines where the TEXT art of the Album/Movie/Application will be displayed in the screen.