public virtual void SetSolidity(
	Solidity Solidity
)

Since solidity is based on tile categories which in turn can contain tiles from multiple tilesets, the same solidity definition can apply to any number of maps with different tilesets. So this doesn't need to be called just to handle tiles from a different tileset, but could be called to make the sprite act differently to all tiles (for example, to suddenly be able to traverse any water).