Coordinates in schematics range from (0,0,0) to (Width-1, Height-1, Length-1).
Schematic: Schematic data.
Width: Size along the X axis.
Height: Size along the Y axis.
Length: Size along the Z axis.
Materials: This is "Classic" for schematics exported from Classic levels, "Pocket" for those from Pocket Edition levels, and "Alpha" for those from Alpha and newer levels.
Blocks: Block IDs defining the terrain. 8 bits per block. Sorted by height (bottom to top) then length then width—the index of the block at X,Y,Z is (Y×length + Z)×width + X.
AddBlocks: Extra bits that can be used to further define terrain; optional. Two nibbles are put into each index in this array. Unlike normal chunks, even indexes go on the high nibble and odd indexes go on the low nibble.
Adddeprecated: Old versions of Schematica used this instead of AddBlocks. Byte array where each byte contains additional data to define terrain, in order. This tag should not be written.
Data: Block data additionally defining parts of the terrain. Only the lower 4 bits of each byte are used. (Unlike in the chunk format, the block data in the schematic format occupies a full byte per block.)