Biomes in order xz.
Additional data for the chunk's block entities (tiles), encoded in the same way as BlockEntityData.nbt is. The position is given by the Int tags x, y, z which are added to the block's compound tag together with the String tag id that contains the name of the tile in pascal case. Wrong encoding or missing tags may result in the block becoming invisible.
Colums where there are world borders (in format xz). This feature hasn't been implemented in the game yet and crashes the client.
Coordinates of the highest block in the column that receives sky light (order xz). It is used to increase the speed when calculating the block's light level.
16x16x16 section of the chunk. The array's keys also indicate the section's height (the 3rd element of the array will be the 3rd section from bottom, starting at y=24). The amount of sections should be in a range from 0 (empty chunk) to 16.
Chunk's blocks, lights and other immutable data.