This file contains a mapping of all block stringy IDs to legacy numeric IDs (which are still used internally, and still needed by third party developers for conversion and for items).
#### Note
Where a block's legacy ID is > 255, its item ID is `255 - legacyBlockId`. This means prismarine stairs = -2 and so on.
This data is obtained by plugging the legacy states into `BlockPalette` in the vanilla BDS using [`pmmp/mapping`](https://github.com/pmmp/mapping), and writing the resulting NBT state obtained.
#### Schema
The following structure is repeated until EOF. There is **no** length prefix, so you have to read to EOF to read all the mappings.
| type | description |
|------|-------------|
| unsigned varint32 | r12 block string ID length |
| byte[] | r12 block string ID |
| little-endian int16 | r12 block metadata |
| TAG_Compound (varint format) | current version NBT blockstate corresponding to the given r12 block |
An example of how to read this file using the PocketMine-MP core library can be seen on the [stable branch](https://github.com/pmmp/PocketMine-MP/blob/41f7c07703bf3f7ef2d9504bbdbdf74257e75d12/src/pocketmine/network/mcpe/convert/RuntimeBlockMapping.php#L71-L86) or on the [master branch](https://github.com/pmmp/PocketMine-MP/blob/master/src/network/mcpe/convert/RuntimeBlockMapping.php#L74-L86).