MVF Default Style

The default style extension for an MVF. A DefaultStyle has things like color, height and opacity and the geometry it should be applied to. It is geared towards rendering the MVF in a 3D mapping engine, but specific properties like color may be useful in other contexts.

If a geometry is NOT referenced by a style, or some other style-like extension, it should generally NOT be rendered by default.

In particular, it is expected that Geometry of kind area will not get a default style, but there may be other cases.