The Sponge Schematic Format Specification
The goal of the Sponge Schematic Format is to improve upon the previous MCEdit Schematic Format to provide better forward compatibility and improve inter compatibility between different versions, platforms, and varyingly modded environments. This format may be used to serialize regions of a minecraft world to disk to be placed back into the world later. It supports all types of modded blocks and block states as well as serializing Entities and TileEntities with the block data.
Current Version - 1
The current version of the Sponge Schematic Specification is 1 - and can be found here.