Block a user
v12 structure
The constants and format are in src/cryptonote_basic/tx_extra.h
2 is "extra nonce" 4 is data length in bytes The next 4 bytes are an ASCII duck The 0 is the "no signature" rct type
Unchanged from monero.
v12 structure
This has not changed from Monero, you can decode it with Monero's code just fine.
It's a duck.