issue 1930 revealed the basic purpose of this sprm, but its layout is unknown.
issue 1291 also contains it and demonstrates that is is merely a container sprm
that contains a list of other undocumented sprms :-). Possibly for efficincy
when introducing a whole set of related new sprms. Stick them all inside one
master undocumented one so that backward compatible readers will skip the master
container 
and all its components. Sprms seem to replace the older mechanism of absolutely
positioning tables with a new way of doing it. And a heap of unknown properties.
Need to update the d608 parser to at least parse the known bits correctly.