I see the definitions of these types from the docs:

swDocASSEMBLY	2
swDocDRAWING	3
swDocIMPORTED_ASSEMBLY	7; Multi-CAD
swDocIMPORTED_PART	6; Multi-CAD
swDocLAYOUT	5
swDocNONE	0
swDocPART	1
swDocSDM	4

All of them seem self explanitory except swDocSDM. What is that type?