from OGC-SFS section 6.1.13.1:
The geometric interiors of any two Surfaces in a MultiSurface may not intersect in the full coordinate system. The boundaries of any two coplanar elements in a MultiSurface may intersect, at most, at a finite number of Points. If they were to meet along a curve, they could be merged into a single surface. MultiSurface is an instantiable class in this Standard, and may be used to represent heterogeneous surfaces collections of polygons and polyhedral surfaces. It defines a set of methods for its subclasses. The subclass of MultiSurface is MultiPolygon corresponding to a collection of Polygons only. Other collections shall use MultiSurface.
OGC-SFS doesn't have a composite type direclty, as ISO and GML have. Although the PolyhedralSurface can be seen as one such case.