Constant MAX_USER_COINBASE_DATA_LEN 

pub(crate) const MAX_USER_COINBASE_DATA_LEN: usize = _; // 86usize

The maximum length of the user-configurable extra_coinbase_data.

The coinbase data is the marker, separator, and user data in a single push, so the user portion is MAX_MINER_DATA_LEN minus the marker, separator, and the 2-byte OP_PUSHDATA1 opcode (for pushes over 75 bytes).