"checkpoints" file structure

[Green Lantern]

What is "checkpoints" file structure http://i59.fastpic.ru/big/2013/0928/f0/6c9c27c2adbb2a178be2cc294aed35f0.jpg ? I mean what kind of data should be put here? Do any docs about exist?

[Andreas Schildbach]

It is best described by the class CheckpointManager in bitcoinj. Have a look at the constructor for how the file format is read.

[Green Lantern]

It is best described by the class CheckpointManager in bitcoinj. Have a look at the constructor for how the file format is read.

Thanks. I have seen it. And I have a question.
Checkpoint size is 96 (Block.HEADER_SIZE + CHAIN_WORK_BYTES + 4 = 80 + 12 +4). So checkpoint is data of block (header) + chainwork bytes + length.
What data for example is in header?
Which exactly kind of blocks should I chooce for adding as headers? What is chainwork bytes and length?